Medical management of patients with angina pectoris

Effect of propranolol on indices of intermittent myocardial ischemia, assessed by exercise testing and ambulatory ST-segment monitoring

Seventy three patients (63 males and 10 females) aged 41-75 years with established stable exertional angina pectoris were studied in a double-blind fashion to confirm the efficacy of 80 mg propranolol administered three times daily and also to examine its effect on ST-segment changes in the electrocardiogram by ambulatory ST-segment monitoring and exercise testing using on-line computer analysis. During ambulatory monitoring, episodes of ST-segment depression in lead CM5 were significantly reduced from 6.5 +/- 0.7 during placebo to 3.4 +/- 0.6 during propranolol therapy (p less than 0.001). The total duration of ST-segment depression was also significantly reduced and the maximal depth of ST-segment depression improved from 2.6 +/- 0.2 mm during placebo to 1.7 +/- 0.2 mm during propranolol therapy (p less than 0.001). The mean +/- SEM exercise time of 5.5 +/- 0.2 minutes on placebo increased to 8.6 +/- 0.4 minutes on propranolol 240 mg daily (p less than 0.001). The 1 mm ST-segment depression time of 3.5 +/- 0.2 minutes on placebo in lead CM5 was prolonged to 6.2 +/- 0.3 minutes during propranolol therapy (p less than 0.001). Propranolol treatment significantly reduced the resting and maximal heart rates (p less than 0.001). The maximal ST-segment depression during exercise in lead CM5 was reduced from 2.3 +/- 0.1 mm on placebo to 1.9 +/- 0.1 mm with propranolol (p less than 0.01). Similarly, the rate-pressure product at peak exercise of 188 +/- 5 units on placebo was reduced to 144 +/- 3 units with propranolol (p less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial exchange of metabolites after nitroglycerin in patients with coronary artery disease

We studied the effects of sublingual nitroglycerin (dose range 0.5-1.0 mg) on cardiac metabolism in the resting state in 12 patients with chronic coronary artery disease. Seven patients with chronic coronary artery disease served as a control group. No patient from either of the groups experienced angina pectoris during the study. Reduced heart work after nitroglycerin was evident from a 34% decrease of oxygen uptake (P less than 0.001) and a 35% fall in coronary sinus blood flow (P less than 0.01). Nitroglycerin decreased lactate extraction by 30% (P less than 0.05), lactate uptake by 58% (P less than 0.025); glucose uptake by 47% (P less than 0.01) while net exchange of free fatty acids did not change. The aorto-coronary sinus difference of plasma citrate became increasingly negative (from -4 +/- 3 mumol/l to -8 +/- 2 mumol/l) (P less than 0.02) after nitroglycerin. In the control group coronary sinus blood flow and myocardial exchange of oxygen and substrates remained unchanged. Our results suggest a relatively increased myocardial utilization of free fatty acids compared with that of carbohydrates after nitroglycerin. This may in part be explained as an inhibition of glycolysis due to citrate accumulation. The study indicates that myocardial lipid-carbohydrate metabolism is disturbed in chronic coronary artery disease even in patients without clinical evidence of ischaemia in resting state and that nitroglycerin reverses this condition towards the metabolism of the normal heart.

Increased coronary sinus lactate concentration during pacing induced angina pectoris after clinical improvement by glyceryl trinitrate

Ten patients with stable angina pectoris and obstructed coronary arteries (greater than 75% reduction in diameter) were studied before and during two periods of pacing, the second of which was preceded by sublingual administration of glyceryl trinitrate (mean dose 0.78 mg). Coronary sinus blood flow measurements and aortocoronary sinus blood sampling for metabolite determinations were carried out. Although the rate of pacing was increased by 10 beats/minute after glyceryl trinitrate administration, the onset of angina was delayed in eight patients during pacing. Drug administration decreased coronary sinus blood flow by 42% and myocardial oxygen uptake by 41% during pacing and induced a shift in mean lactate extraction towards a net release (from 3.1% to -12.6%). It increased the number of patients producing lactate from three to five. Glyceryl trinitrate administration decreased myocardial glucose uptake throughout the study, decreased lactate extraction during recovery, and increased the aortocoronary sinus citrate gradient at rest and during recovery, while the exchange of free fatty acids remained unchanged. A decrease in aortocoronary sinus lactate difference during pacing after glyceryl trinitrate administration correlated positively with the fall in coronary sinus blood flow. The metabolic data do not indicate an augmented myocardial lactate production after glyceryl trinitrate administration. A decrease in coronary sinus blood flow seems, therefore, to be of primary importance in explaining the elevated coronary sinus lactate concentration. Our finding that coronary sinus lactate concentration increased during pacing after glyceryl trinitrate administration despite clinical improvement questions the validity of its use as a quantitative index of ischaemia.

Influence of propranolol on uptake of radioiodinated heptadecanoic acid and thallium-201 in the dog heart

In an experimental study, the influence of propranolol on myocardial uptake of radioiodinated heptadecanoic acid (131I-HDA) and thallium-201 (201Tl) in the dog heart was assessed. Uptake of 131I-HDA and 201Tl was evaluated in ten control dogs and in ten dogs 20 min after IV administration of propranolol (0.15 mg/kg). In both groups, four healthy dogs were studied and six dogs were studied after coronary artery occlusion. It was shown that both total uptake of 131I-HDA and 201Tl did not alter significantly, regardless of significant changes in hemodynamic parameters and total arterial plasma FFA levels. However, distribution of both 131I-HDA and 201Tl was markedly affected by propranolol, since the endocardial to epicardial ratio showed significantly higher values in the ischemic myocardial regions. The results of our study indicate that propranolol (1) preserves myocardial perfusion in the normal and acutely ischemic dog heart, and (2) gives a more favorable distribution in the ischemic myocardial region towards the subendocardial layers.

Patterns of disturbed myocardial perfusion in patients with coronary artery disease. Regional myocardial perfusion in angina pectoris

Fifty patients who presented with angina pectoris were studied to examine the disturbances of regional myocardial perfusion during stress. Each patient underwent 16-point precordial mapping of the ECG during an exercise test, and coronary and left ventricular angiography. Regional myocardial perfusion was assessed using an atrial pacing test and a short-lived radionuclide, krypton-81m. Eleven patients had negative exercise tests and uniform increases in myocardial activity of krypton-81m of 98 +/- 18.0% during pacing. Ten patients performed 30,000-43,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and increases in myocardial activity of krypton-81m to remote and jeopardized myocardium at the onset of pacing. However, further pacing produced a decrease in activity in the affected segment of 68.0 +/- 9.0% accompanied by ST-segment depression and angina. Twelve patients achieved 26,000-32,000 J in positive exercise tests and had significant coronary artery disease. Atrial pacing produced increased activity of krypton-81m to remote myocardium. The jeopardized segment at first showed no change and then a decrease in regional activity of krypton-81m (89.0 +/- 17%) accompanied by ST-segment depression and chest pain. Seventeen patients achieved only 7000-22,000 J in positive exercise tests. These patients showed abnormal coronary anatomy and developed decreases in regional activity of krypton-81m to the affected segment of myocardium starting at the onset of atrial pacing and decreasing by 88 +/- 0 7.0% below control. We conclude that different patterns of disturbed myocardial distribution of krypton-81m are present during stress-induced ischemia in patients with coronary artery disease. There was a close temporal relationship between these disturbances and ST-segment depression.

Plasma concentrations and bioavailability of isosorbide dinitrate and pindolol from a combination formulation

The plasma concentrations and bioavailability of sustained-release isosorbide dinitrate and standard-release pindolol have been compared after administration of these drugs in combination and alone. Bioavailability parameters of isosorbide dinitrate and pindolol obtained after administration of the drugs in combination were not significantly different (P greater than 0.05) to those obtained after administration of either drug alone. Two peaks of mean concentrations of isosorbide dinitrate occurred in plasma after administration of 30 mg of this drug in combination with 7.5 mg pindolol (4.4 ng ml-1 at 1 h and 4.5 ng ml-1 at 5 h), or alone (5.9 ng ml-1 at 2 h and 5.7 ng ml-1 at 5 h). In each case, plasma concentrations of isosorbide dinitrate were maintained during at least 8 h, whereas the drug was not detected in plasma at 2.5 h after administration of a standard-release formulation. The peaks of mean concentrations of pindolol were 39.7 ng ml-1 at 1.5 h after administration of 7.5 mg drug in combination with isosorbide dinitrate and 38.0 ng ml-1 at 1 h administration of the drug alone. Concentrations of pindolol in plasma declined with a half-life of 3 h.

Effect of a calcium inhibitor, nifedipine, on exercise tolerance in patients with angina pectoris: a double-blind study

The effect of nifedipine on exercise tolerance was studied in 30 patients with stable angina and positive graded exercise testing. Treadmill exercise testing was performed on each of five consecutive days. Placebo or nifedipine, 10 mg sublingually, was given 30 minutes before exercise on the third day. The following day the intervention was reversed in a double-blind manner. Angina was abolished by nifedipine but not by placebo in 12 patients (40 percent). The time to onset of angina in the remaining patients increased from 4.1 +/- 0.4 (SEM) to 6.7 +/- 0.6 min (p less than .001). Time to ST depression greater than or equal to 2 mm increased from 4.0 +/- 0.3 to 5.4 +/- 0.5 min, while duration of exercise increased from 6.3 +/- 0.3 to 8.2 +/- 0.4 min (p less than .001). The maximum heart rate was 145 +/- 3.3 with nifedipine and 122 +/- 3.8 min-1 with placebo (p less than .01). Resting systolic blood pressure decreased 30 min after nifedipine administration from 131 +/- 3.4 to 106 +/- 2.9 mm Hg (p less than .01). Maximal systolic blood pressure during exercise was lower with nifedipine (127 +/- 4.8 mm Hg) than with placebo (155 +/- 5.6 mm Hg, p less than .01). We conclude that nifedipine significantly improves the exercise tolerance of patients with stable angina pectoris by decreasing peripheral vascular resistance and myocardial oxygen demand.

The beneficial effect of the beta blocker timolol in stable agina pectoris

Timolol is a new beta blocker with cardioselective properties. A single blind controlled study was performed to assess the efficacy of timolol maleate in doses of 10 to 30 mg per day in 20 patients affected by stable angina pectoris. The patients received a placebo for a baseline period of 2 weeks, followed by 12 weeks of timolol. The number of anginal attacks dropped from 14.9 attacks per week in the baseline period to a minimum of 4.6 attacks per week in the sixth week of treatment (P less than 0.01). The number of tablets of nitroglycerin taken per week was reduced from 6.5 during the baseline period to 2.3 in the sixth week of treatment. Resting heart rate decreased from a baseline mean value of 72 beats per minute to 51.7 and 53.7 per minute at weeks 6 and 12 respectively (P less than 0.01). Blood pressure both at rest and during exercise was significantly reduced. The mean work index measured during bicycle ergometry was 127 units before treatment; it increased by 29.4 units and 36.1 units during week 6 and week 12 respectively (P less than 0.05). There was a marked symptomatic improvement in 50% of the patients. Mild fatigue was a common side effect but it disappeared following reduction of dose. We concluded that timolol maleate significantly reduces the number of anginal attacks and increases the work capacity of patients affected by stable angina pectoris

Myocardial ischaemia in patients with frequent angina pectoris

One hundred patients with angina pectoris underwent 16-point electrocardiographic (ECG) mapping of the left hemithorax during a standardised exercise test. Forty-five patients had maximum ST-segment depression at position V5, while 35 had no ECG signs of ischaemia at this position. In 20 V5 was on the edge of the precordial area, which showed less severe ST-depression than the central positions. An Oxford ECG recorder and highspeed analyser were modified and used in 50 of the patients with daily angina for recording ST-segment changes over 24 hours. Serial 24-hour ambulatory recordings from the edge of the precordial area of ischaemia identified during exercise detected a mean of only 14 +/- SD 3% of the episodes of ST-segment changes recorded from the centre of the same area. Only 16 +/- 2% of the episodes detected by ECG were accompanied by chest pain. More episodes occurred between 4 am and 6 am than at any other time during the night. This study shows the importance of recording ECG evidence of ischaemia from the precordial position showing maximum changes during exercise. ECG evidence of ischaemia occurs more frequently than anginal pain. These objective measurements add important information to the frequency of chest pain reported by patients with ischaemic heart disease.

Medical therapy of angina pectoris

The pathophysiology of angina pectoris is best understood as an imbalance between oxygen supply and demand. The primary determinants of myocardial oxygen demand are heart rate, arterial pressure, heart size, myocardial contractility, and myocardial mass. The medical therapy of angina pectoris is directed toward reducing myocardial oxygen demand by reducing the workload of the heart and the specific determinants listed. The most common medications used in the treatment of angina pectoris are nitroglycerin and propranolol. Nitroglycerin reduces myocardial oxygen demand primarily by reducing heart size and arterial pressure. Propranolol reduces oxygen demand primarily by reducing heart rate. Medical therapy is generally effective in controlling the symptoms of angina pectoris in 80% or more of the patients and allows them to lead useful and productive lives.

Transient asymptomatic S-T segment depression during daily activity

The significance of asymptomatic episodes of ischemic type S-T segment depression was studied in 20 patients with coronary heart disease. Continuous 10 hour electrocardiographic recordings accompanied by detailed daily diaries of activity and symptoms were obtained periodically during a mean time of 16 months. All patients had ischemic type S-T depression associated with angina pectoris during treadmill exercise. Measurements of heart rate, S-T depression and exercise level at the onset of angina obtained during repeated controlled exercise tests at the start of each study period were compared with the measurements recorded during daily activity. After 2,826 hours of recording, 411 transient epidsodes of ischemic type S-T depression were noted during usual daily activity. Only 101 (25 percent) of these episodes were associated with angina. The remaining episodes were unrelated to other symptoms or to posture. All occurred at heart rates significantly lower than those observed at the onset of angina during exercise testing. Of these episodes of asymptomatic S-T depression, 72 percent occurred only at rest or during very light activity such as slow walking or sitting. Nitroglycerin administered hourly significantly reduced the frequency of these episodes, thus supporting the concept that they represent painless ischemia. Because the episodes of asymptomatic ischemic type S-T depression occurred more frequently than angina during usual daily activity and were evident at heart rates and activity levels well below those expected to evoke ischemia, they may be caused by factors other than those that cause angina.

Effects of propranolol on coronary hemodynamic and metabolic responses to tachycardia stress in patients with and without coronary disease

To clarify the influence of propranolol-and particularly its heart-rate effects-on myocardial ischemia, coronary hemodynamics and metabolism were studied in 15 patients utilizing a protocol to control heart rate. Ten patients had significant coronary narrowing (CAD) and 5 were normal. Systemic pressure, coronary sinus blood flow (CSBF), left ventricular oxygen utilization (LVVO2), ST Segment depression, and myocardial lactate extraction were measured before and after propranolol (10 mg IV), at rest, during pacing-induced tachycardia stress. Propranolol-related reduction in CSBF and LVVO2 at rest was reversed when heart rate was controlled in both patient groups. Propranolol failed to alter heart-rate threshold, tension-time index (TTI), CSBF, or LVVO2 at angina in the CAD patients. Likewise, ischemic-type ST depression, decreases in lactate extraction, and coronary resistance were unchanged compared to values observed during tachycardia stress before propranolol. In normal coronary patients, propranolol also produced no significant change in LVVO2 or coronary resistance when its heart rate effects were controlled. These data imply that a major coronary and metabolic influence of propranolol relates to changes occurring secondary to its influence on heart rate. Furthermore, this agent's anti-ischemic effect is not prominent during tachycardia stress suggesting that this stress test may be clinically useful in patients taking propranolol.

The role of vasodilator therapy in heart failure

This article has attempted to summarize the current status of the therapeutic use of vasodilator drugs in acute and chronic heart failure. It is apparent from the increasing number of publications in this area that this alternative to more standard forms of therapy is likely to find a permanent and important place in the management of patients with heart disease. It should also be apparent that ideal drugs for the therapy of chronic heart failure are not yet available. Nevertheless, it is probable that such drugs will emerge and become at least as important as the routine use of digitalis in such patients.

The aetiology of non-exertional angina pectoris

The occurrence of angina pectoris while at rest, although long recognized, has not been satisfactorily explained. In the non-exertional attacks studied there was an increase in heart load, as estimated by the product of heart rate and systolic pressure. Angina occurred when the load exceeded a critical level. Recumbency was associated with 94% of non-exertional attacks; 58% followed a meal; in 54% both factors were present. It is suggested that recumbency causes an increase in heart load because of expansion of blood volume by transfer of fluid from interstitial spaces, and that a meal does so because of digestive activity.

Heart rate and arterial blood pressure during exercise in patients with angina pectoris. Effects of training and of nitroglycerin

In 29 patients with typical exertional angina pectoris, intra-arterial systolic blood pressure (SBP), heart rate (HR), and the rate-pressure product (RPP = HR X SBP X 10(-2) were continuously recorded during repeated bouts of leg or arm exercise. Development of chest pain was independent of the workload and occurred at a fairly constant value of RPP, of HR, and of SBP in each patient for a given type of exercise, but the pain threshold values for all three variables were consistently higher during arm exercise than during leg exercise. The reproducibility of the pain threshold values was assessed for leg exercise. The variation, based on individual coefficients of variation, ranged from 1.3% to 13% (group mean, about 6%). There was no significant difference between the SBP values obtained by the traditional, noninvasive cuff technique and the values during intra-arterial monitoring. In 25 patients a physical training program of an average of three months increased the maximal amount of work (watt X sec) performed before onset of pain by 100%. The most conspicuous effect of training on cardiac function was a 10% reduction of HR at a given workload, SBP being unchanged. Over-all, the data suggest that the increased exercise capacity caused by training could be accounted for by the reduction in the relation between RPP and external workload. The improvement in exercise capacity resulting from training was on the same level of magnitude as the 90% increase obtained in 11 untrained patients after administration of 0.25 to 0.50 mg of nitroglycerine sublingually prior to exercise. In contrast to the finding after training, nitroglycerin administered to subjects increased HR by 10%, but reduced SBP by 13%, RPP remaining unchanged. Therefore to explain the effect of nitroglycerin on exercise capacity additional economizing changes in myocardial performance (e.g., reduction of heart volume) are required.

Oral nitroglycerin as a prophylactic antianginal drug: clinical, physiologic, and statistical evidence of efficacy based on a three-phase experimental design

With the use of a three-phase experimental design, the efficacy of oral nitroglycerin has been evaluated in a total of 53 patients with documented angina pectoris due to coronary artery disease. The study were a double-blind, randomized, and cross-over comparison of controlled-release nitroglycerin (2.6 mg. tablets administered three times daily) and an indistinguishable placebo. Sixteen patients recorded anginal symptoms by the diary method over a 6 month trial of randomly sequenced 1 month periods of drug or placebo. In 15 patients, ST segments were monitored with a Holter dynamic electrocardiograph for periods of 10 to 12 hours under normal life style and evaluated by matching activities during periods of drug and placebo. In 22 patients, a multistage treadmill exercise test was conducted to an endpoint of anginal pain. The three phases of the investigation were run in succession; each phase was completed before the next one was begun. Oral nitroglycerin reduced the incidence and severity of anginal attacks by 47.2 and 49.4 per cent, respectively, and decreased the number of sublingual nitroglycerin tablets used by 51.1 per cent in comparison to placebo (p less than 0.001). Eleven of 16 patients (69 per cent) decreased their need for sublingual nitroglycerin by over 50 per cent. Based on a polynomial trend analysis over a period of 8 weeks, no tolerance to the therapeutic effects of the drug was found. With DCG monitoring, drug decreased the ST segment depression from 1.76 mm. on placebo to 1.12 mm, with a significant difference of 0.64 mm. (p less than 0.001). ST segment depression was decreased more than 0.5 mm. by drug in comparison to placebo in 10 of 15 patients (66 per cent). Larger depressions of the ST segment noted with placebo at heart rates greater than 80 beats per minute were prevented by administration of the drug. During treadmill exercise, drug delayed the onset of pain by 83 seconds (64 per cent) over placebo (p less than 0.001) and decreased the duration of pain by 70 seconds (49 per cent) in comparison to placebo (p less than 0.001). Drug did not affect heart rate or systolic blood pressure at rest or after exercise, as well as rate-pressure product for production of angina following exercise (p less than 0.05). There was no side effects reported caused by the drug. The data demonstrate that oral nitroglycerin, given as controlled-release tablets, was absorbed from the gastrointestinal tract in quantities sufficient to provide statistically significant clinical improvement of angina pectoris.

Effects of nitroglycerin on the major determinants of myocardial oxygen consumption. An angiographic and hemodynamic assessment

A direct and quantitative study of the effects of sublingually administered nitroglycerin on the major determinants of myocardial oxygen consumption was carried out in 10 patients, 7 with coronary artery disease. Left ventricular wall tension, estimates of the contractile state and heart rate were studied directly using simultaneous pressure measurements and angiographically obtained volume determinations. The peak systolic left ventricular wall tension decreased 15 percent after administration of nitroglycerin, suggesting a diminished myocardial oxygen requirement. Increased myocardial oxygen requirements were suggested by the occurrence of both positive chronotropic and inotropic effects. Heart rate increased 15 percent. The mean circumferential fiber shortening velocity increased 26 percent and the ejection fraction 30 percent; these findings, in association with a 23 percent reduction in left ventricular end-diastolic volume, were considered consistent with an increase in the contractile state. The mechanism of action of nitroglycerin seems to relate best to the decrease in systolic wall tension. The end-diastolic tension decreased 57 percent, suggesting the possibility that diastolic coronary blood flow may be augmented by diminished extravascular resistance to flow.

The effect of aortocoronary bypass grafts on myocardial blood flow reserve and treadmill exercise tolerance

Twenty-five patients had myocardial blood flow reserve determinations (percentage increase in myocardial blood flow with stress), treadmill exercise tests and coronary and bypass cineangiography pre- and postaortocoronary bypass surgery. Twenty of the patients had the postoperative studies performed three months after operation, three at two months and two at five and six months, respectively.

Eleven of the 25 patients had all significant coronary artery obstructions (75% or greater) bypassed and all grafts were open at the time of restudy. Preoperatively, blood flow reserve had been abnormal in nine and all had positive treadmill tests. Postoperatively, all eleven patients had normal myocardial blood flow response to stress and treadmill tests were negative in ten (one patient was not restudied on the treadmill).

In six patients, no patent grafts could be demonstrated. These patients continued to show abnormal blood flow reserve and positive treadmill studies.

Eight of the 25 patients had partial revascularization in that some grafts were open, some closed, and some significantly occlusive lesions were not bypassed. Four of these eight patients had normal flow and treadmill studies and the remainder continued to have an abnormal response to one or both of the measurements.

The relationship between treadmill exercise response, myocardial blood flow reserve, and graft patency was significant at the 0.005 level for patients with all grafts open or closed. No significant correlation was obtained between any of the measurements in those patients with partial revascularization.

The data indicate that successful aortocoronary bypass grafting provides myocardial revascularization as reflected in a return to normal of the myocardial blood flow reserve and response to treadmill stress testing.

Myocardial blood flow in coronary artery disease. Effect of right atrial pacing and nitroglycerin

Sixteen patients, 10 with significant three-vessel coronary artery disease (>50% occlusion of each vessel) and six without coronary disease, had nutrient myocardial blood flow, cardiac output, pressure time/min and arterial pressure determinations at rest, with atrial pacing and with right atrial pacing plus nitroglycerin. In the patients with coronary disease, nutrient myocardial blood decreased an average of 16% ( P < 0.001) with pacing alone but increased by 22% ( P < 0.001) from the pacing flows with the addition of 0.4 mg sublingual nitroglycerin at the same pacing rate. The directional changes in myocardial blood flow were unrelated to perfusion pressure or pressure work. In the patients without coronary disease, opposite effects were observed. With right atrial pacing, nutrient myocardial blood flow increased by 23% ( P < 0.02). With the addition of nitroglycerin, myocardial blood flow decreased by 15% ( P < 0.02). These changes were directionally related to changes in pressure-work of the heart It is suggested that the findings in this study are consistent with observations made in the experimental animal which indicate that the effect of nitroglycerin may be partly due to a redistribution of myocardial blood flow.

Coronary artery occlusion in the conscious dog. Effects of alterations in arterial pressure produced by nitroglycerin, hemorrhage, and alpha-adrenergic agonists on the degree of myocardial ischemia

Nitroglycerin is generally believed to be contraindicated during acute myocardial infarction because the resultant decrease in coronary perfusion pressure and reflex tachycardia might extend the area of ischemia. To determine the effects of nitroglycerin and alterations in arterial pressure on the degree of myocardial ischemia, the left anterior descending coronary artery was occluded for repeated 15-min periods in closed-chest conscious dogs. The degree of myocardial ischemia was estimated by summating the S-T segment elevation (∑ST) recorded from 12 myocardial electrodes. Although heart rate increased and arterial pressure decreased, ∑ST after 15 min of coronary occlusion was 14 ± 3 mv ( P < 0.02) less during nitroglycerin therapy than during control occlusions. When the same alteration in arterial pressure was produced by venous hemorrhage, ∑ST tended to be greater than during control occlusions (+14 ± 7 mv, ns ); the difference between the nitroglycerin and hemorrhage interventions was highly significant (28 ± 9 mv, P < 0.02). ∑ST was also less than control when phenylephrine was administered in doses sufficient to increase arterial pressure 25 mm Hg (–16 ± 3 mv, P < 0.005) and 50 mm Hg (–15 ± 2 mv, P < 0.001). When the decrease in arterial pressure and reflex tachycardia induced by nitroglycerin were reversed by simultaneous infusion of methoxamine, ∑ST was greatly reduced from control (–50 ± 16 mv, P < 0.02) and was significantly less than that occurring during nitroglycerin alone (–25 ± 5 mv, P < 0.001). We conclude that nitroglycerin may be a useful agent during acute myocardial infarction, particularly when the fall in coronary perfusion pressure and increase in heart rate are prevented by the simultaneous administration of an alpha-adrenergic agonist.