Is Your Horse at Risk? The Silent Heart Problems Owners Miss

Your horse’s heart powers everything from everyday movement to top-level performance. It is at the center of their vitality and longevity. Whether your goal is to get your horse in tip-top shape for competition or to ensure they live comfortably into their senior years, cardiovascular health is a non-negotiable.

This article explores the science of equine heart health, explains common cardiac conditions, and offers practical strategies backed by research to keep your horse’s heart strong.

Inside the Equine Heart

The equine cardiovascular system is a finely tuned engine designed for power, speed, and endurance. Horses are among nature’s most remarkable athletes, and their heart is the foundation of that capacity.

Anatomy and Physiology

The horse’s heart, like a human’s, has four chambers: right and left atria (receiving chambers) and right and left ventricles (pumping chambers). Oxygen-poor blood enters the right atrium, is pumped to the right ventricle, and then travels to the lungs where oxygen exchange occurs. Oxygen-rich blood then flows into the left atrium, enters the left ventricle, and is pushed into the aorta, the largest artery, to supply the entire body.

One unique adaptation in horses is their Purkinje fiber system, which is more extensive than in humans. This allows electrical impulses to spread quickly through the ventricles, producing a forceful and coordinated contraction that is essential for sustaining galloping speeds for miles.

Size and Capacity

The average horse heart weighs between 7 and 10 pounds, about 1 percent of their body weight (Reef, 1995). That may not sound huge, but in terms of power output, it is extraordinary. At rest, a horse’s cardiac output (the amount of blood pumped per minute) is around 25 liters, but during peak exercise it can exceed 300 liters per minute (Young & Marlin, 1988). For comparison, an elite human athlete peaks at about 25 to 30 liters.

Legendary racehorse Secretariat reportedly had a heart weighing nearly 22 pounds, which contributed to his unmatched stamina and speed.

Role in Movement and Metabolism

During exercise, the cardiovascular system ensures that oxygen is delivered to the muscles while waste products like carbon dioxide and lactic acid are removed. Horses also have a splenic reservoir that stores extra red blood cells. During intense exercise, these cells can be released to boost oxygen-carrying capacity by up to 50 percent (Persson, 1967). This adaptation makes horses some of the most efficient oxygen-utilizing mammals on earth.

Common Cardiovascular Issues in Horses

Even though horses’ hearts are designed for performance, they can face several health challenges.

Heart Murmurs

Heart murmurs are abnormal sounds caused by turbulent blood flow through valves or defects. While some are harmless “physiologic murmurs,” others may indicate conditions like valve regurgitation or congenital defects.

Arrhythmias

Arrhythmias, or irregular rhythms, are surprisingly common. Atrial fibrillation is the most frequent, especially in Thoroughbreds and Standardbreds. Horses with AFib may show poor recovery after exercise, fatigue, or even collapse. Fortunately, treatment with quinidine sulfate or electrical cardioversion can often restore normal rhythm (McGurrin et al., 2005).

Myocarditis

Myocarditis (inflammation of the heart muscle) often stems from viral or bacterial infections. Research has linked equine influenza and equine herpesvirus to myocarditis (Decloedt et al., 2012). This condition can cause sudden performance decline or even sudden death if untreated.

Congenital Defects

Congenital defects like ventricular septal defects (VSDs) occur in foals. Some are small and compatible with a normal lifespan, while larger defects can cause heart failure. Early detection with echocardiography is key.

Exercise-Induced Collapse

Exercise-related cardiac collapse, although rare, can be linked to arrhythmias or genetic neuromuscular disorders. Cases of sudden cardiac death in Thoroughbred racing are under study, with genetics increasingly implicated (Kapusniak et al., 2024).

Signs of a Struggling Heart

Cardiac disease in horses is often subtle until it becomes serious. Watch for:

• Poor performance or early fatigue: a hallmark of reduced oxygen delivery.

• Irregular heartbeat or pulse: best detected with a stethoscope or ECG.

• Lethargy or weakness: especially if sudden.

• Coughing or labored breathing: may indicate fluid buildup in the lungs (pulmonary edema).

• Swelling (edema): particularly in the lower limbs or abdomen, from circulatory compromise.

If you notice these signs, call your veterinarian promptly.

Protecting Your Horse’s Heart

Routine Veterinary Exams

Veterinary evaluation is the frontline defense. Common diagnostic tools include:

• Auscultation: listening with a stethoscope.

• Electrocardiography (ECG): records electrical activity and identifies arrhythmias.

• Echocardiography: ultrasound imaging of chambers, valves, and blood flow.

• Exercise testing: heart monitoring during controlled exercise can reveal hidden abnormalities.

Monitoring Heart Rate at Home

Resting heart rate in adult horses is 28 to 44 bpm. During maximal exertion, it may reach 220 to 240 bpm. Recovery rate, or how quickly heart rate drops after exercise, is a strong indicator of fitness. A slow recovery can suggest cardiovascular compromise.

Fitness and Conditioning

Gradual conditioning is key. Interval training, which alternates work and rest, helps improve stroke volume (amount of blood pumped per beat) without overstraining the heart. Research shows that horses conditioned with interval training develop greater aerobic capacity and more efficient oxygen utilization (Evans, 2007).

Weight Management

Obesity increases strain on the heart and raises the risk of Equine Metabolic Syndrome (EMS). A 2023 study confirmed that EMS is often linked to systemic hypertension, which stresses the equine heart (Stefaniuk-Szmukier et al., 2023).

Supporting Heart Health Through Nutrition

Diet plays a critical role in cardiovascular resilience.

• Selenium and Vitamin E: Deficiency can contribute to oxidative stress and muscle disorders like nutritional myopathy. Adequate levels protect both skeletal and cardiac muscle (Finno & Valberg, 2012).

• Omega-3 fatty acids: Have anti-inflammatory effects and support vascular health. Elzinga et al. (2019) demonstrated improved insulin sensitivity in horses with metabolic syndrome after omega-3 supplementation.

• Balanced electrolytes: Sodium, potassium, and chloride are critical for heart conduction and muscle contraction. Deficiencies can predispose horses to arrhythmias.

• Avoiding excess starch and sugar: Reduces obesity and metabolic syndrome risk, protecting long-term cardiovascular health.

Advancements in Equine Cardiology

Equine cardiology is rapidly advancing, offering new tools for early detection and treatment.

• Portable ECG monitors: Allow vets and trainers to detect arrhythmias during real-time exercise, not just at rest.

• Doppler Echocardiography: Provides detailed images of blood flow and valve function, making diagnosis more precise.

• Genetic Research: Studies have identified heritable risk factors for sudden cardiac death, especially in racing breeds (Kapusniak et al., 2024). This may eventually allow for genetic screening of at-risk horses.

• Biomarkers: Blood tests measuring cardiac troponins are being studied as non-invasive indicators of heart muscle injury (Slack et al., 2012).

  
  

Final Thoughts

Heart health is one of the most important, yet often overlooked, aspects of equine care. Horses are natural athletes, but even the strongest heart can be vulnerable. By combining regular veterinary care, thoughtful training, balanced nutrition, and awareness of warning signs, owners can give their horses the best chance at a long, strong, and healthy life.

The bottom line: early action saves lives. If something feels off, do not hesitate to call your vet. And if your horse is healthy now, consistent monitoring and care will help keep it that way.

References

• Decloedt, A. et al. (2012). Arrhythmias and Myocarditis in Horses: Clinical Relevance and Diagnosis.

• Elzinga, S. et al. (2019). Effects of omega-3 fatty acid supplementation on insulin sensitivity in horses with metabolic syndrome.

• Evans, D. (2007). Physiology of equine performance: key adaptations for exercise.

• Finno, C., & Valberg, S. (2012). Nutrition and neuromuscular disorders in horses.

• Kapusniak, L. et al. (2024). Genetic risk factors in sudden cardiac death in Thoroughbreds.

• McGurrin, M. C. H., et al. (2005). Atrial fibrillation in horses: treatment and prognosis.

• Persson, S. G. B. (1967). On blood volume and work capacity in horses.

• Reef, V. B. (1995). Equine cardiovascular ultrasonography.

• Slack, J., et al. (2012). Cardiac troponin as a biomarker in horses.

• Stefaniuk-Szmukier, M. et al. (2023). Equine Metabolic Syndrome and Hypertension.

• Young, L. E., & Marlin, D. J. (1988). Cardiac output and performance in Thoroughbreds.

• UTCVM Medical Center. Heart Rate Ranges in Horses.