Heart Murmur in Dogs: Symptoms, Causes & Treatment

Dr. Jason Gagné, DVM, DACVIM
By Dr. Jason Gagné, DVM, DACVIM
Updated: 5/9/20242-4 minutes
veterinarian using stethoscope on chocolate labrador dog

A heart murmur in dogs can be serious, but it’s not necessarily cause for alarm. Here’s what you should know about this cardiovascular condition.

What is a Heart Murmur in Dogs?

Heart murmurs refer to an unusual sound that’s detected when listening to a dog’s heartbeat through the stethoscope. Instead of the regular heart sounds, there may be a “whooshing” noise indicating an abnormal blood flow through the heart.

Heart murmurs in dogs vary in severity, from manageable to life-threatening. So, it’s important to talk to your veterinarian about your dog’s symptoms to determine what type of medical help is needed. 

What Are the Symptoms of a Heart Murmur in Dogs? 

A heart murmur is usually a symptom of an underlying heart abnormality. Some dogs with a heart murmur will not show any indications of heart disease. However, dogs diagnosed with heart disease may present any of the following signs: 

  • Coughing 

  • Lethargy 

  • Excessive panting 

  • Fainting 

  • Pale gums 

  • Getting tired quicky

If you notice any of these symptoms, contact your veterinarian as soon as possible. They can assess your pet’s condition and, if a heart murmur is detected, they will let you know the type, grade and the most effective treatment.

The 6 Grades of Heart Murmurs in Dogs

Grade I

Typically, Grade One heart murmurs are barely audible and usually the least serious of all grades. Your veterinarian may decide to monitor a Grade One murmur, or they may advise further evaluation.

Grade II

These murmurs are slightly more audible, but still soft in intensity. 

Grade III

Grade Three murmurs are more easily detected through the stethoscope and may indicate underlying health conditions. 

Grade IV

Grade Four murmurs are easy to hear with a stethoscope and are somewhere between grades Three and Five in intensity.

Grade V

Heart murmurs that are so loud they can be felt by resting your hand against the dog’s chest are classified as Grade Five. The vibrations that you may feel as the heart pumps are known as a “thrill.”

Grade VI

The most intense murmurs are often a sign of significant heart disease.

Your veterinarian may be able to hear a Grade Six murmur through their stethoscope without even placing it directly on the chest. Sometimes Grade Six murmurs are so loud that they can even be detected without the help of a stethoscope. 

The volume of your dog’s heart murmur can help your veterinarian come up with a diagnostic plan. Another important part of the consultation is understanding what type of murmur your dog is experiencing.

Types of Heart Murmurs

Your veterinarian will listen to your dog’s heart through a stethoscope to determine when the murmur occurs, how long it lasts, and what part of the heart it’s coming from.

The murmur can occur when the heart muscle contracts (systolic murmurs), in between heart beats when the muscle is relaxed (diastolic murmurs), or continuously throughout the heartbeat cycle. They can also be long or short, start loud and get quieter, or manifest in a crescendo. 

All these details are important in establishing what exactly is causing the abnormal noise in your dog’s heartbeat.

What Causes Heart Murmur in Dogs?

You might think that heart disease is the cause behind unusual heartbeat sounds. Although this is often the case, there are other possible conditions leading to heart murmurs (called physiologic murmurs). Here are some of the possible causes of physiologic heart murmurs: 

  • Anemia 

  • Low blood proteins 

  • Fever 

  • Hyperthyroidism

Heart Murmur in Puppies

Puppies can also experience heart murmurs. This can happen in all shapes and sizes of young dogs, including large breed puppies.

Many puppy heart murmurs are referred to “innocent flow murmurs” or physiologic heart murmurs. They are low in intensity (so can only be detected by your veterinarian with their stethoscope) and don’t usually require medical intervention. 

Innocent flow murmurs in puppies often disappear completely before the canine is six months old. However, check with your veterinarian to make sure the unusual heart sound is benign, and not a medical condition that needs urgent attention.

In rare cases, your puppy might have a heart murmur as a result of a congenital heart problem. These are often (but not always) quite loud. They are likely to require both regular monitoring and medical or even surgical intervention.

How Are Heart Murmurs Treated?

If the heart murmur is low in intensity, your veterinarian may recommend close monitoring with or without medical treatment. Physiologic murmurs in puppies will often resolve on their own.

Where necessary, your veterinarian will recommend a treatment plan based on the underlying condition, whether it’s anemia, hyperthyroidism or heart disease.

You can also ask your veterinarian if dog heart-health supplements are appropriate for your pet, as they can support heart and vascular function. 

Follow your veterinarian’s instructions and continue to look out for any new symptoms. In many cases, heart murmurs in dogs will not stop your pet living a long and happy life.

Remember that prompt intervention is often key to keeping your pet healthy, so don’t forget to schedule regular veterinarian visits for your dog.

For more expert tips on caring for your canine companion, explore our other dog health articles.

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