Heart Murmurs in Horses

Published Dec. 17, 2024
Vet using a stethoscope on a grey horse

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A horse heart murmur is an abnormal heart sound produced by turbulent blood flow. Heart murmurs are a symptom of an underlying health issue in a horse—typically heart disease.

Some horse heart murmurs are congenital (present at birth) and can be heard in newborn foals, while other horses may develop murmurs due to cardiac disease later in life.

While any horse may develop a murmur, some may be predisposed to certain heart conditions that can cause murmurs, including Arabians and Friesians.

Other horses may have a heart murmur and not have any clinical signs associated with it.

Key Takeaways

  • Heart murmurs are typically a sign of an underlying heart issue.
  • A heart murmur may sound like whooshing or blowing when listening to a horse’s heart with a stethoscope.
  • Horses with heart murmurs may be prescribed diuretics, ACE inhibitors, or other medications suggested by your veterinarian, depending on the underlying condition.
  • Work with your veterinarian to determine if a horse with a heart murmur is OK to ride.

What Is a Heart Murmur in Horses?

A heart murmur is an irregular heart sound typically caused by abnormal blood flow within the heart. A normal heartbeat has a “lub dub, lub dub” sound, but a heart murmur sounds like a whooshing, blowing, or honking noise that can be heard with a stethoscope.

Unless the murmur is severe, most heart murmurs can only be heard via stethoscope. Not all heart murmurs are indicative of a heart disease; many horses can live long and relatively normal lives even with a murmur present.

Murmurs are most frequently noted in senior horses or high-performing athletes. However, if you notice potential symptoms of a heart murmur in your horse, call your veterinarian out for an examination.

Horse Heart Anatomy

To understand heart murmurs in horses, it’s important to understand how a normal horse heart works.

In a horse’s heart, there are four chambers:

  • The two upper chambers—the left and right atria—store blood.

  • The two lower ventricles pump blood out of the heart to the lungs and body.

The left side of the heart pumps blood to the body to supply oxygen to organs, muscles, and other tissues. This blood comes back to the right side of the heart, so it can be pumped to the lungs to expel waste and become re-oxygenated.

For the heart to pump blood through the body, it must first relax for blood to pass through the atria and fill the ventricles. During the contraction phase, the ventricles squeeze and push blood on to its next destination.

If a horse has a heart murmur, this means one or more of the functions in the process above do not work correctly. This can be due to factors like holes in the heart, or blood that is moving in the opposite direction it should be while pumping through the heart, due to weak or poorly functioning valves.

Symptoms of Heart Murmur in Horses

Signs of a heart murmur in a horse largely depend on the underlying health condition affecting them. In addition to the heart murmur, a horse may also experience:

  • Exercise intolerance

  • Depression

  • Increased heart rate for extended periods unrelated to exercise

  • Increased respiratory rate or effort

  • Cough, especially with congestive heart failure when fluid begins to back up into the lungs

  • Weight loss

  • Edema or swelling of the chest or abdomen

  • Visible jugular pulse that extends more than halfway up the neck

  • Weakness or collapse

  • Sudden death

Causes of Heart Murmur in Horses

The most common conditions that cause heart murmurs in horses include:

  • Patent ductus arteriosus (PDA): A condition where the blood vessel that connects the aorta and pulmonary artery (ductus ateriorsus) does not close after birth, causing a congenital murmur. PDA can be a “normal” congenital murmur in newborn foals for the first week of life.

  • Ventricular septal defect (VSD): A hole in the wall between the lower heart chambers. This is a common condition in newborn foals. If there is a hole present at birth, it should close within the first two weeks after a foal is born; if it does not, this could be problematic. This condition is more common in Standardbreds, Arabians, and Welsh Ponies.

  • Valve regurgitation: This is when a heart valve does not close properly, causing blood to backflow. This condition causes murmurs that can be normal, particularly in racehorses that have high volumes of blood pumping through the heart at increased rates. It can also be due to age-related degeneration or infection. Types of valve regurgitation in horses include:

    • Mitral regurgitation (mitral insufficiency), when the mitral valve doesn’t close completely. It’s the most common cause of cardiac failure in horses.

    • Pulmonary regurgitation is a leak between the right ventricle and the pulmonary artery.

    • Aortic regurgitation (aortic insufficiency) is when the aortic valve does not close properly, allowing blood to leak back into the heart. This is the most common valve to develop murmurs in older horses.

    • Tricuspid regurgitation is a type of right-sided heart valve dysfunction.

How Do Veterinarians Detect a Heart Murmur in Horses?

Murmurs are generally first noticed during a physical exam with a stethoscope. Veterinarians can characterize the sound and note the location, timing, and intensity.

If a murmur is identified, your veterinarian may suggest blood work to check for other abnormalities like anemia or infection.

Your veterinarian may recommend tests such as an electrocardiography (ECG) to record the heart’s electrical activity, or a Doppler echocardiogram ultrasound to monitor the flow of blood through the heart. These can help determine the severity of turbulent blood flow and also visualize damaged or weakened heart valves.

Treatment of Heart Murmurs in Horses

Treatment of a heart murmur in a horse depends on the underlying health condition causing it.

Your veterinarian may prescribe some medications to help slow the heart disease process or make your horse more comfortable, especially if they’re a senior or experiencing heart failure.

Some medications your veterinarian may discuss could include:

  • Diuretics like furosemide to help lower their blood pressure

  • ACE inhibitors or acepromazine, which act as vasodilators (medications that help relax blood vessel walls to improve blood flow) to reduce the heart’s strain keeping up with the blood flow

  • Digoxin, which may help strengthen the heart during its contraction phase

Recovery and Management of Heart Murmurs in Horses

The murmurs will dissipate in horses experiencing them during episodes of dehydration, anemia, or colic once they recover from their illness.

Other murmurs tend to increase in severity over time as a horse ages, the heart disease worsens, as valves degenerate or scar, or as a horse puts excessive strain on weak valves through high exercise loads.

Many horses do not experience exercise intolerance with murmurs, and senior horses may not have any negative consequences due to their weak valves.

Heart murmurs are a symptom of an underlying health issue in a horse—typically heart disease.

However, some horses may develop heart failure over time and require medication and management to keep them comfortable. This may include reducing or stopping exercise, medications as mentioned above, or dietary changes.

As with humans, horses experiencing heart failure should have limited salt intake. If your horse likes to stand and lick at the salt block all day, your veterinarian may recommend adding the minimal necessary amount to their daily grain and remove the free-choice option.

Adding omega supplements to the diet can help support the cardiovascular system.

If a horse is experiencing advanced heart failure and is having trouble breathing or stops eating or drinking, humane euthanasia may be recommended due to their poor quality of life.

Heart Murmur in Horses FAQs

How long can a horse live with a heart murmur?

Most horses with a heart murmur will live somewhat normal lives with minimal effect on life expectancy, depending on the underlying cause of the heart murmur. However, horses that develop murmurs at a younger age may have a shorter life expectancy or more complications.

Horses with aortic regurgitation are at higher risk for sudden death even at a young age.

Can you ride a horse with a heart murmur?

Depending on the type of heart murmur, your horse may be ridden or exercised if your veterinarian deems it safe. They will likely recommend rechecks more frequently for these horses to monitor the murmur and their overall wellness.

If the heart murmur is causing decreased function of the heart or lungs, however, it may not be advisable to ride your horse.

What does the heart murmur in a horse sound like?

Heart murmurs as heard through a stethoscope may sound musical, like whooshing, buzzing, or honking.

References

Judd B. Toxins Can Cause Heart Disease in Horses. Veterinary Partner. 

Marr C, Bowen I. Cardiology of the Horse. Saunders/Elsevier. 2010.

Heart Murmurs in Horses. Large Animal Hospital, College of Veterinary Medicine, University of Florida. 

Kriz NG, Hodgson DR, Rose RJ. Prevalence and clinical importance of heart murmurs in racehorses. Journal of the American Veterinary Medical Association. May 1, 2000.

Cunningham S, Roderick K. Introduction to heart and blood vessel disorders of horses. Merck Veterinary Manual.

References


Courtnee Morton, DVM, CVA, CVC

WRITTEN BY

Courtnee Morton, DVM, CVA, CVC

Veterinarian

Dr. Courtnee Morton is a 2017 Ross University School of Veterinary Medicine graduate. Since graduation, she completed an equine internship...


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