Effects of formaldehyde on cardiovascular system in in situ rat hearts

Survival of formalin intoxication in a 13-year-old Thoroughbred gelding

BACKGROUND

Formalin intoxication via the gastrointestinal route has not been previously reported in the horse. Whereas ingestion of formalin in humans, although rare, is well documented. Majority of human cases are either accidental, suicidal or homicidal and often lead to fatality, with a reported lethal formaldehyde dose equating to 0.12 - 0.16 g/kg bwt.

OBJECTIVES

To describe a single case report of the clinical management of an adult horse referred to a veterinary teaching hospital following accidental administration of 10% formalin via nasogastric tube.

METHODS

A 13-year-old Thoroughbred gelding originally presented to the referring veterinarian for colic where 1.8 L of 10% formalin was accidentally administered instead of mineral oil via nasogastric intubation, a potentially lethal dose of formaldehyde (0.12 g/kg bwt). Approximately 20-hours following 10% formalin administration the horse was admitted to the referral hospital with moderate tachycardia, occasional ectopic beats, tacky and hyperaemic mucous membranes, delayed capillary refill time, reduced borborygmi, and pronounced digital pulses. Diagnostic investigations included laboratory blood analysis, urinalysis, electrocardiogram, abdominal ultrasound, palpation per rectum and gastroscopy.

RESULTS

Patient assessment found evidence of toxicity to the gastrointestinal tract, hypovolaemia and risk for laminitis. Intensive care included fluid and electrolyte therapy, anti-inflammatories and analgesia, continuous digital cryotherapy, gastro-protectants and other methods of gastrointestinal support. The horse was discharged from hospital on day 14 with no long-term complications and the client-veterinarian relationship was preserved.

DISCUSSION

In human cases of ingestion, gastrointestinal injury is typically accompanied by severe metabolic acidosis and multiple organ dysfunction syndrome due to toxicity of other body systems that can contribute to non-survival. Formaldehyde toxicity in the present case predominantly affected the gastrointestinal tract, most likely a direct result of the route of administration. Aside from gastrointestinal injury, primary toxicity of other body systems was not confirmed. To prevent this medical error recurring, the referring veterinary clinic revised their labelling and storage of 10% formalin.

CONCLUSION

This is the first report of systemic formalin intoxication in the horse. Following a high dose of 10% formalin (0.12 g/kg bwt formaldehyde) enterally, the horse survived having received intensive supportive care based on human guidelines for ingested formalin.

Formaldehyde induced the cardiac damage by regulating the NO/cGMP signaling pathway and L-Ca2+ channels

Background

Formaldehyde (FA) is a common environmental pollutant that has been found to cause negative cardiovascular effects, however, the toxicological mechanism is not well understood. In this study, we investigated the molecular effects of the Nitric Oxide (NO)/cyclic Guanosine Monophosphate (cGMP) signaling pathway and L-type calcium (L-Ca2+) channels in rat hearts.

Methods

We designed the short-term FA exposure on the rat heart in different concentrations (0, 0.5, 3, 18 mg/m3). After 7 days of exposure, the rats were sacrificed and the rat tissues were removed for various experiments.

Results

Our experimental data showed that FA resulted in the upregulation NO and cGMP, especially at 18 mg/m3. Further, when exposed to high concentrations of FA, Cav1.2 and Cav1.3 expression decreased. We conclude that the NO/cGMP signaling pathway and downstream related channels can be regulated by increasing the production of NO in the low concentration group of FA. High concentration FA directly regulates L-Ca22+ channels.

Conclusion

This study suggests that FA damages the function of the cardiovascular system by regulating the NO/cGMP signaling pathway and L-Ca2+ channels.

Associations between e-cigarette use or dual use of e-cigarette and combustible cigarette and metabolic syndrome: results from the National Health and Nutrition Examination Survey (NHANES)

PURPOSE

Examine associations between e-cigarette use or dual use of e-cigarette and combustible cigarette and metabolic syndrome (MetS).

METHODS

Cross-sectional data of 5121 U.S. adults from the National Health and Nutrition Examination Survey were analyzed. Weighted multivariable Poisson regression models were used to examine associations between e-cigarette use or dual use and MetS and its components. Prevalence ratios (PRs) with 95% confidence intervals (95% CI) were estimated.

RESULTS

Current and former e-cigarette users were 30% (95% CI: 1.13, 1.50) and 15% (95% CI: 1.03, 1.28) more likely to have MetS than never e-cigarette users. Current or former e-cigarette use was also associated with elevated triglycerides, reduced high-density lipoprotein (HDL) cholesterol, and elevated blood pressure (AOR ranged from 1.15 to 1.42, all P < 0.05). The prevalence of MetS for dual users was 1.35-fold (95% CI: 1.15, 1.58) higher than that for never smokers and 1.21-fold (95% CI: 1.00, 1.46) higher than that for combustible cigarette-only users. Dual users were also more likely to report elevated triglycerides and reduced HDL cholesterol than never smokers or combustible cigarette-only users (all P < 0.05).

CONCLUSIONS

E-cigarette use or dual use is associated with MetS. Our findings may inform tobacco control policies regarding regulations of e-cigarette use.

Fossil-fuel and combustion-related air pollution and hypertension in the Sister Study

Hypertension is a leading risk factor for disease burden, with more than 200 million disability-adjusted life-years attributed to high blood pressure in 2015. While outdoor air pollution is associated with cardiovascular disease, the joint effect of exposure to air pollution from combustion products on hypertension has rarely been studied. We conducted a cross-sectional analysis to explore the association between combustion-related air pollution and hypertension. Census-tract levels of ambient concentrations of nine fossil-fuel and combustion-related air toxics (biphenyl, naphthalene, polycyclic organic matter, diesel emissions, 1,3-butadiene, acetaldehyde, benzene, acrolein, and formaldehyde) from the 2005 National Air Toxics Assessment database and NO2 from 2005 monitoring data were linked to baseline residential addresses of 47,467 women in the Sister Study cohort. Hypertension at enrollment (2003-2009) was defined as high systolic (≥140 mm Hg) or diastolic (≥90 mm Hg) blood pressure or taking antihypertensive medication. We used log-binomial regression and quantile-based g-computation to estimate the individual and joint effects of fossil-fuel and combustion-related air pollution on hypertension. Comparing the highest to lowest quartiles, diesel emissions (prevalence ratio (PR) = 1.05, 95% confidence interval (CI) = 1.01,1.08), 1,3-butadiene (PR = 1.04, 95%CI = 1.00,1.07), acetaldehyde (PR = 1.08, 95%CI = 1.04,1.12), benzene (PR = 1.05, 95%CI = 1.02,1.08), formaldehyde (PR = 1.08, 95%CI = 1.04,1.11), and NO2 (PR = 1.08, 95%CI = 1.05,1.12) were individually associated with higher prevalence of hypertension. The PR for the joint effect of increasing all ambient air toxics and NO2 by one quartile was 1.02 (95%CI = 1.01,1.04). Associations varied by race/ethnicity, with stronger associations observed among women reporting races/ethnicities (Hispanic/Latina, non-Hispanic Black and other) other than non-Hispanic White. In conclusion, we found that air pollution from fossil fuel and combustion may be a risk factor for hypertension.

Electronic Cigarette Use and the Risk of Cardiovascular Diseases

Electronic cigarettes or e-cigarettes are the most frequently used tobacco product among adolescents. Despite the widespread use of e-cigarettes and the known detrimental cardiac consequences of nicotine, the effects of e-cigarettes on the cardiovascular system are not well-known. Several in vitro and in vivo studies delineating the mechanisms of the impact of e-cigarettes on the cardiovascular system have been published. These include mechanisms associated with nicotine or other components of the aerosol or thermal degradation products of e-cigarettes. The increased hyperlipidemia, sympathetic dominance, endothelial dysfunction, DNA damage, and macrophage activation are prominent effects of e-cigarettes. Additionally, oxidative stress and inflammation are unifying mechanisms at many levels of the cardiovascular impairment induced by e-cigarette exposure. This review outlines the contribution of e-cigarettes in the development of cardiovascular diseases and their molecular underpinnings.

Quinolizinium-based fluorescent probes for formaldehyde detection in aqueous solution, serum, and test strip via 2-aza-Cope rearrangement

Formaldehyde is an abundant contaminant in food and environments causing various diseases. Thus, the development of fast, simple, and selective formaldehyde detection is of great interest. Herein, novel quinolizinium-based fluorescent probes were designed based on a 2-aza-Cope rearrangement reaction and showed high selectivity to formaldehyde by fluorescence emission shift. We successfully reduced the detection time by increasing the bulkiness of the homoallylic moiety. The probes were applied to detect formaldehyde in aqueous solution, serum, and paper format.

The cellular function and molecular mechanism of formaldehyde in cardiovascular disease and heart development

As a common air pollutant, formaldehyde is widely present in nature, industrial production and consumer products. Endogenous formaldehyde is mainly produced through the oxidative deamination of methylamine catalysed by semicarbazide-sensitive amine oxidase (SSAO) and is ubiquitous in human body fluids, tissues and cells. Vascular endothelial cells and smooth muscle cells are rich in this formaldehyde-producing enzyme and are easily damaged owing to consequent cytotoxicity. Consistent with this, increasing evidence suggests that the cardiovascular system and stages of heart development are also susceptible to the harmful effects of formaldehyde. Exposure to formaldehyde from different sources can induce heart disease such as arrhythmia, myocardial infarction (MI), heart failure (HF) and atherosclerosis (AS). In particular, long-term exposure to high concentrations of formaldehyde in pregnant women is more likely to affect embryonic development and cause heart malformations than long-term exposure to low concentrations of formaldehyde. Specifically, the ability of mouse embryos to effect formaldehyde clearance is far lower than that of the rat embryos, more readily allowing its accumulation. Formaldehyde may also exert toxic effects on heart development by inducing oxidative stress and cardiomyocyte apoptosis. This review focuses on the current progress in understanding the influence and underlying mechanisms of formaldehyde on cardiovascular disease and heart development.

Short-term e-cigarette vapour exposure causes vascular oxidative stress and dysfunction: evidence for a close connection to brain damage and a key role of the phagocytic NADPH oxidase (NOX-2)

AIMS

Electronic (e)-cigarettes have been marketed as a 'healthy' alternative to traditional combustible cigarettes and as an effective method of smoking cessation. There are, however, a paucity of data to support these claims. In fact, e-cigarettes are implicated in endothelial dysfunction and oxidative stress in the vasculature and the lungs. The mechanisms underlying these side effects remain unclear. Here, we investigated the effects of e-cigarette vapour on vascular function in smokers and experimental animals to determine the underlying mechanisms.

METHODS AND RESULTS

Acute e-cigarette smoking produced a marked impairment of endothelial function in chronic smokers determined by flow-mediated dilation. In mice, e-cigarette vapour without nicotine had more detrimental effects on endothelial function, markers of oxidative stress, inflammation, and lipid peroxidation than vapour containing nicotine. These effects of e-cigarette vapour were largely absent in mice lacking phagocytic NADPH oxidase (NOX-2) or upon treatment with the endothelin receptor blocker macitentan or the FOXO3 activator bepridil. We also established that the e-cigarette product acrolein, a reactive aldehyde, recapitulated many of the NOX-2-dependent effects of e-cigarette vapour using in vitro blood vessel incubation.

CONCLUSIONS

E-cigarette vapour exposure increases vascular, cerebral, and pulmonary oxidative stress via a NOX-2-dependent mechanism. Our study identifies the toxic aldehyde acrolein as a key mediator of the observed adverse vascular consequences. Thus, e-cigarettes have the potential to induce marked adverse cardiovascular, pulmonary, and cerebrovascular consequences. Since e-cigarette use is increasing, particularly amongst youth, our data suggest that aggressive steps are warranted to limit their health risks.

The Cardiovascular Effects of Electronic Cigarettes

PURPOSE OF REVIEW

Electronic cigarettes (e-cigarettes) are gaining rapid popularity among all age groups, especially among youth. They have evolved into technologically advanced devices capable of delivering nicotine concentration and other substances. In addition to nicotine, e-cigarettes' constituents possess variety of toxic chemicals that have adverse effects on human body.

RECENT FINDINGS

In recent years, steady downward trend in tobacco usage has been observed; however, e-cigarette use is on upward trend. E-cigarettes are advertised as "safer" alternatives to conventional smoking and as an aid to smoking cessation. Emerging studies have, however, shown that e-cigarettes have harmful effects on the cardiovascular system and that most of the e-cigarette users are dual users, concurrently using e-cigarettes and smoking conventional cigarettes. Despite a gap in clinical studies and randomized trials analyzing adverse cardiovascular effects of e-cigarette use, the existing literature supports that different constituents of e-cigarettes such as nicotine, carbonyls, and particulate matters carry potential risk for cardiovascular diseases (CVD) on its users.

Anthracycline-induced cardiomyopathy: cellular and molecular mechanisms

Despite the known risk of cardiotoxicity, anthracyclines are widely prescribed chemotherapeutic agents. They are broadly characterized as being a robust effector of cellular apoptosis in rapidly proliferating cells through its actions in the nucleus and formation of reactive oxygen species (ROS). And, despite the early use of dexrazoxane, no effective treatment strategy has emerged to prevent the development of cardiomyopathy, despite decades of study, suggesting that much more insight into the underlying mechanism of the development of cardiomyopathy is needed. In this review, we detail the specific intracellular activities of anthracyclines, from the cell membrane to the sarcoplasmic reticulum, and highlight potential therapeutic windows that represent the forefront of research into the underlying causes of anthracycline-induced cardiomyopathy.

Electronic Cigarette Use and Blood Pressure Endpoints: a Systematic Review

PURPOSE OF REVIEW

E-cigarettes (e-cigs) release toxic chemicals known to increase blood pressure (BP) levels. The effects of e-cigs on BP, however, remain unknown. Studying BP may help characterize potential cardiovascular risks of short- and long-term e-cig use. We summarized published studies on the association of e-cig use with BP endpoints.

RECENT FINDINGS

Thirteen e-cig trials (12 cross-over designs) and 1 observational study evaluated systolic and diastolic blood pressure (SBP and DBP). All trials included at least one e-cig arm with nicotine, 6 a no-nicotine e-cig arm, and 3 a placebo arm. SBP/DBP increased in most nicotine e-cig arms, in some non-nicotine e-cig arms, and in none of the placebo arms. The observational study followed e-cig users and nonsmokers for 3.5 years with inconsistent findings. The use of e-cigs with and without nicotine may result in short-term elevations of both SBP and DBP. Prospective studies that investigate the long-term cardiovascular impact of e-cig use are needed.

The outbreak of methanol intoxication during COVID-19 pandemic: prevalence of brain lesions and its predisposing factors

During the COVID-19 pandemic, methanol-containing beverages' consumption has risen because people mistakenly believed that alcohol might protect them against the virus. This study aimed to evaluate the prevalence and predisposing factors of brain lesions in patients with methanol toxicity and its outcome. A total of 516 patients with confirmed methanol poisoning were enrolled in this retrospective study, of which 40 patients underwent spiral brain computed tomography (CT) scan. The presence of unilateral or bilateral brain necrosis was significantly higher in the non-survival group (p = 0.001). Also, intracerebral hemorrhage (ICH) and brain edema were prevalent among patients that subsequently died (p = 0.004 and p = 0.002, respectively). Lower Glasgow Coma Scale (GCS) was related to a higher mortality rate (p = 0.001). The mortality rate in chronic alcohol consumption was lower than the patients who drank alcohol for the first time (p = 0.014). In conclusion, increasing the number of methanol poisoning and its associated mortality and morbidity should be considered a threat during the COVID-19 pandemic.

Cardiovascular risk of electronic cigarettes: a review of preclinical and clinical studies

Cigarette smoking is the most preventable risk factor related to cardiovascular morbidity and mortality. Tobacco usage has declined in recent years; however, the use of alternative nicotine delivery methods, particularly e-cigarettes, has increased exponentially despite limited data on their short- and long-term safety and efficacy. Due to their unique properties, the impact of e-cigarettes on cardiovascular physiology is not fully known. Here, we summarize both preclinical and clinical data extracted from short- and long-term studies on the cardiovascular effects of e-cigarette use. Current findings support that e-cigarettes are not a harm-free alternative to tobacco smoke. However, the data are primarily derived from acute studies. The impact of chronic e-cigarette exposure is essentially unstudied. To explore the uniqueness of e-cigarettes, we contemplate the cardiovascular effects of individual e-cigarette constituents. Overall, data suggest that exposure to e-cigarettes could be a potential cardiovascular health concern. Further preclinical research and randomized trials are needed to expand basic and clinical investigations before considering e-cigarettes safe alternatives to conventional cigarettes.

Could E-cigarette vaping contribute to heart disease?

INTRODUCTION

E-cigarettes have become a controversial topic. While their benefits are questioned by the scientific community, a part of the medical profession is still supporting them as an effective harm reduction tool for smoking cessation. The impact of E-cigarettes on the cardiovascular system is still elusive.

AREAS COVERED

We assessed results from animal, pre(clinical), and epidemiological studies to critically evaluate and synthesize evidence relevant to the cardiovascular effects of E-cigarettes. Animal studies have demonstrated that E-cigarette vapor exposure can cause endothelial and cardiac dysfunction. However, there have also been reports on the less harmful effects of E-cigarette vapor exposure in comparison to classical tobacco cigarettes. Measurements of flow-mediated dilation in acute human exposure settings have mostly demonstrated that E-cigarettes cause vascular endothelial dysfunction. Epidemiological studies have shown that E-cigarette use is associated with an increased risk for cardiovascular disease, although switching from classical tobacco cigarettes to E-cigarettes can have beneficial cardiovascular effects. Misinterpretation of scientific data by activists on either side is another problem.

EXPERT OPINION

In conclusion, we need more and better (pre)clinical data comparing the health effects of E-cigarette vaping as compared with tobacco cigarette smoking, in order to counsel the legislation for better health policies.

Biological Toxicity of the Compositions in Electronic-Cigarette on Cardiovascular System

Using electronic cigarette (e-cig) among youth is becoming a critical public health crisis in the USA. However, the biological impacts of the e-cig on multiple organ systems, especially in the cardiovascular system, are largely unknown. Unlike conventional tobacco, e-cig combines various chemical ingredients including nicotine and other add-on non-nicotine chemicals, such as the solvents (propylene glycol and/or vegetable glycerin) and flavoring chemicals, which dramatically increases the diversity of the potential implications. The recent outbreak of e-cig vaping-related tragic deaths in youth and multiple hospitalized patients raised a question on the safety of e-cig use and led to an urgent need for the knowledge of the health risk of the e-cig compositions. Therefore, in the review, we summarized the latest findings from both human and animal studies on the potential cardiovascular toxicological effects of e-cig on the cardiovascular system in terms of the systemic physiological implications and the cellular and molecular mechanisms involved.

Vasodilatory effect of formaldehyde via the NO/cGMP pathway and the regulation of expression of KATP, BKCa and L-type Ca2+ channels

Formaldehyde (FA), a well-known toxic gas molecule similar to nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H₂S), is widely produced endogenously via numerous biochemical pathways, and has a number of physiological roles in the biosystem. We attempted to investigate the vasorelaxant effects of FA and their underlying mechanisms. We found that FA induced vasorelaxant effects on rat aortic rings in a concentration-dependent manner. The NO/cyclic guanosine 5' monophosphate (cGMP) pathway was up-regulated when the rat aortas were treated with FA. The expression of large-conductance Ca²⁺-activated K⁺ (BK_Ca) channel subunits α and β of the rat aortas was increased by FA. Similarly, the levels of ATP-sensitive K⁺ (K_ATP) channel subunits K_ir6.1 and K_ir6.2 were also up-regulated when the rat aortas were incubated with FA. In contrast, levels of the L-type Ca²⁺ channel (LTCC) subunits, Ca_v1.2 and Ca_v1.3, decreased dramatically with increasing concentrations of FA. We demonstrated that the regulation of FA on vascular contractility may be via the up-regulation of the NO/cGMP pathway and the modulation of ion channels, including the upregulated expression of the K_ATP and BK_Ca channels and the inhibited expression of LTCCs. Further study is needed to explore the in-depth mechanisms of FA induced vasorelaxation.

Formaldehyde produced from d-ribose under neutral and alkaline conditions

Formaldehyde is toxic and has been implicated in the pathologies of various diseases, such as cognitive impairment and cancer. Though d-ribose is widely studied and provided as a supplement to food such as flavor and drinks, no laboratories have reported that d-ribose is involved in the formaldehyde production. Here, we show that formaldehyde is produced from d-ribose in lysine or glycine solution and Tris-HCl buffer under neutral and alkaline conditions. Intraperitoneal injection of C57BL/6J mice with d-ribose significantly increased the concentration of brain formaldehyde, compared to the injection with d-glucose or saline. These data suggest that formaldehyde levels should be monitored for the people who take d-ribose as a supplement.

Inhalation of Simulated Smog Atmospheres Affects Cardiac Function in Mice

The health effects of individual criteria air pollutants have been well investigated. However, little is known about the health effects of air pollutant mixtures that more realistically represent environmental exposures. The present study was designed to evaluate the cardiac effects of inhaled simulated smog atmospheres (SA) generated from the photochemistry of either gasoline and isoprene (SA-G) or isoprene (SA-Is) in mice. Four-month-old female mice were exposed for 4 h to filtered air (FA), SA-G, or SA-Is. Immediately and 20 h after exposure, cardiac responses were assessed with a Langendorff preparation using a protocol consisting of 20 min of global ischemia followed by 2 h of reperfusion. Cardiac function was measured by index of left-ventricular developed pressure (LVDP) and cardiac contractility (dP/dt) before ischemia. Pre-ischemic LVDP was lower in mice immediately after SA-Is exposure (52.2 ± 5.7 cm H₂O compared to 83.9 ± 7.4 cm H₂O after FA exposure; p = 0.008) and 20 h after SA-G exposure (54.0 ± 12.7 cm H₂O compared to 79.3 ± 7.4 cm H₂O after FA exposure; p = 0.047). Pre-ischemic left ventricular contraction dP/dt_max was lower in mice immediately after SA-Is exposure (2025 ± 169 cm H₂O/sec compared to 3044 ± 219 cm H₂O/sec after FA exposure; p < 0.05) and 20 h after SA-G exposure (1864 ± 328 cm H₂O/sec compared to 2650 ± 258 cm H₂O/sec after FA exposure; p = 0.05). In addition, SA-G reduced the coronary artery flow rate 20 h after exposure compared to the FA control. This study demonstrates that acute SA-G and SA-Is exposures decrease LVDP and cardiac contractility in mice, indicating that photochemically-altered atmospheres affect the cardiovascular system.

Formaldehyde regulates vascular tensions through nitric oxide-cGMP signaling pathway and ion channels

Formaldehyde (FA) has been linked to the detrimental cardiovascular effects. Here, we explored the effects and mechanisms of FA on rat aortas both in vivo and in vitro. The results presented that FA evidently lowered the blood pressures of rats. The expression levels of BK_Ca subunits α and β1 and iNOS of the aortas were up-regulated by FA in vivo. However, FA markedly reduced the levels of Ca_v1.2 and Ca_v1.3, which are the subunits of L-Ca²⁺ channel. Furthermore, the contents of NO, cGMP and iNOS in the aortas were augmented by FA. To further confirm these findings, the mechanisms accredited to these effects were examined in vitro. The data showed that FA contracted the isolated aortic rings at low concentrations (<300 μM), while it relaxed the rings at high concentrations (>500 μM). The FA-induced vasoconstriction at low concentrations was blocked partly by an inhibitor of ACE. The relaxation caused by FA at high concentrations was attenuated by the inhibitors of NO-cGMP pathway, L-Ca²⁺ channel and BK_Ca channel, respectively. Similarly, the expression of iNOS was strongly enhanced by FA in vitro. The effects of FA on the aortic rings with endothelium were significantly greater than those on the rings without endothelium. Our results indicate that the vasoconstriction of FA at low concentrations might be partially pertinent to endothelin, and the FA-caused vasorelaxation at high concentrations is possibly associated with the NO-cGMP pathway, L-Ca²⁺ channel and BK_Ca channel. This study will improve our understanding of the pathogenic mechanisms for FA-related cardiovascular diseases.

Preparation of viable adult ventricular myocardial slices from large and small mammals

This protocol describes the preparation of highly viable adult ventricular myocardial slices from the hearts of small and large mammals, including rodents, pigs, dogs and humans. Adult ventricular myocardial slices are 100- to 400-μm-thick slices of living myocardium that retain the native multicellularity, architecture and physiology of the heart. This protocol provides a list of the equipment and reagents required alongside a detailed description of the methodology for heart explantation, tissue preparation, slicing with a vibratome and handling of myocardial slices. Supplementary videos are included to visually demonstrate these steps. A number of critical steps are addressed that must be followed in order to prepare highly viable myocardial slices. These include identification of myocardial fiber direction and fiber alignment within the tissue block, careful temperature control, use of an excitation-contraction uncoupler, optimal vibratome settings and correct handling of myocardial slices. Many aspects of cardiac structure and function can be studied using myocardial slices in vitro. Typical results obtained with hearts from a small mammal (rat) and a large mammal (human) with heart failure are shown, demonstrating myocardial slice viability, maximum contractility, Ca²⁺ handling and structure. This protocol can be completed in ∼4 h.