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Heart Murmurs in Dogs and Cats
Heart murmurs are common and do not always have to be sinister. However, heart murmurs should be evaluated because they may signal a heart problem or other health issue.

What does it mean?

A heart murmur is a whooshing sound heard through a stethoscope when blood flows through the heart valves. It simply indicates that there is some turbulent flow in the heart that can be heard.  Heart murmurs are common and do not always have to be sinister. However, heart murmurs should be evaluated because they may signal a heart problem or other health issue.

When the heart beats, valves open and close, allowing blood to flow. When the valves close, they produce two sounds: a “lub” and a “dub”. If your veterinarian can hear a whooshing sound between these two heart sounds, this is called a heart murmur.

A murmur may mean you pet has a heart problem but heart murmurs are also present in healthy dogs and cats so they are not a reason to panic. These are called “innocent” or “physiologic” heart murmurs.

Can you hear the heart murmur?

A grade 6 is so loud it can be felt (feels a like your phone vibrating in your pets chest) and can be heard with the stethoscope held off the chest. Grade 4-6 heart murmurs are unlikely to be innocent and should be evaluated.

You will usually not be able to hear the heart murmur as a stethoscope is required for this. Your veterinarian will classify your pets murmur from grade 1-6. Grade 1 is so soft that it can only be heard when listening very carefully in a quiet room.

Symptoms and Causes

A murmur is caused by turbulent or abnormal blood flow across the heart valves. Innocent murmurs are common in young kittens and puppies as their blood is a little thinner than adult animals. This can result in turbulence when the heart contracts. An innocent puppy murmur usually disappears by 16 weeks of age. An innocent puppy or kitten murmur is usually soft (grade 1-3). If your veterinarian classifies your pets murmur as a grade 4, 5 or 6, this is very unlikely to be innocent and should be evaluated.

Other causes of innocent or physiologic murmurs include stress or anaemia in adult animals. Heart murmurs are also common in normal Sighthounds (Greyhounds, Whippets, Borzois, Salukis) due to increased cardiac output in these athletic breeds.

Cardiac causes of heart murmurs include valve leaks due to degeneration of the heart valves, thickening of the heart muscle (hypertrophic cardiomyopathy), failure of the heart muscle (dilated cardiomyopathy), or congenital cardiac disease (your pet was born with an abnormality). Any dog or cat greater than 16 weeks of age or if the heart  murmur is grade 4 or louder in a younger pet, should have the heart evaluated by a cardiologist to check for pathologic cardiac disease.