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HEART MURMURS in cats & dogs

Lots of people assume that a ‘heart murmur’ is a disease or a diagnosis. This is not true – a heart murmur is simply a noise that your vet has heard through the stethoscope. It tells us that blood is not flowing smoothly through the heart for some reason and is making more noise than normal. Bay Vets explains more.



There are lots of different reasons why a cat or dog might develop a heart murmur.

Some are caused by birth defects in the heart, for example a ‘hole in the heart’, and are often heard first in puppies or kittens when they have vaccinations. Some of these murmurs resolve as the puppy or kitten grows.

Diseased valves in the heart tend to leak, and they make a noise when they do which is heard as a heart murmur. This is quite common in older dogs and cats.

Heart muscle disease (so called ‘Cardiomyopathy’) can occur at almost any age in cats and dogs, and it tends to deform heart valves making them leak. This will, in turn, cause a heart murmur.

Some heart murmurs are termed ‘innocent’ or ‘flow’ murmurs. They are usually quite quiet and are not caused by any disease process, but are a variation of normal. The murmur is just the sound of blood flowing through the heart, which in some individuals can be louder than others – particularly in thin fit animals such as greyhounds and lurchers.

Finally, heart murmurs can be caused by disease elsewhere in the body. For example, if a cat or dog does not have enough red blood cells (anaemia) then the blood can become very thin, and this can make more noise as it flows through the heart, causing a murmur to be heard.



It is common for cats and dogs to have heart murmurs but no other signs at all. In this situation it is advisable to find out what is the cause of the murmur?

If the cause of the murmur can be found, then your vet can give you the best advice about management of any heart problem. Cats and dogs with heart murmurs and no symptoms often need no medication, but sometimes they do require treatment that can help prevent worsening of any disease process that is going on.

For an accurate diagnosis, it is usually necessary to perform Echocardiography – which is a complicated way of saying an ultrasound scan of the heart, which is the same sort of scan that humans have for pregnancy diagnosis. It is harmless to your pet, and only involves a little clipping of hair on either side of the chest low down so that the ultrasound probe can contact the skin. In most dogs sedation is not needed. Some cats can be successfully scanned without any sedative, but they tend to be a bit more wriggly, and we often find that a low dose of a safe sedative drug enables the cardiologist to get much more information from the scan.

Ultrasound means that we can look right inside your pet’s heart. We can see the valves, heart muscle, blood vessels etc, and we can even measure blood flow in areas of the heart and see blood flowing in colour. This means that we can find the cause of the heart murmur in most cases, and the cardiologist can give you the best advice on management.


Depending upon your individual pet, the heart rate, rhythm, pulse, loudness of murmur, breed, age etc, the vet may advise other tests including:

Blood pressure – usually in older dogs, or cats with heart muscle disease, kidney problems, diabetes or thyroid problems.

E.C.G. – short for electro-cardio-gram. This looks at the electrical impulses that pass through the heart muscle as it beats and can be very useful for helping work out if there is any problem with the heart rhythm.

Blood tests – various tests can be useful – it is often useful to check that the rest of the body is working well, especially the kidneys and liver, before we dispense any drugs, and we can even find out if the heart muscle has been damaged.


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