Q. My veterinarian told me that my cat has a heart murmur. Does this mean he will die prematurely from heart disease?
A. Dear Karen: Your concern is understandable. But some feline heart murmurs don’t mean anything dire at all. And while some may be signs of a serious problem, the problem can often be treated, with the cat having many wonderful, comfortable years ahead of him. A murmur indicates only that there is blood flow turbulence somewhere in the heart or in the great vessels that are leaving the heart, and this can result from many different things.
A kitten, for instance, may have what is known as an “innocent” murmur that he outgrows. In fact, it’s very common for a kitten to have a soft murmur in the first months of life. Experts don’t exactly understand why, but one theory is that kittens are slightly anemic compared to adult cats and that blood with a lower red blood cell concentration tends to be a bit more turbulent. Then, too, since kittens don’t have much body fat, turbulent blood flow is easier to hear through a stethoscope. Older cats may occasionally develop soft heart murmurs, too, due to anemia, fever or other systemic illness.
An adult cat with a murmur might also have disease of the heart muscle, called cardiomyopathy. The most common type of cardiomyopathy in cats is hypertrophic cardiomyopathy, characterized by thickening of the heart muscle. That prevents the muscle from fully relaxing, thus limiting the amount of blood the heart can pump. The loudness of the murmur depends on where the muscle thickens. Murmur or not, cardiomyopathy often leads to congestive heart failure and may need to be treated with medicine to slow the progression of the disease. Appropriately treated cats can live a long time, often years, with a good quality of life.
Murmurs are graded on a scale of one to six for loudness or intensity. A grade one is so quiet that even an experienced listener can hear it only after a few minutes in a quiet room. A grade six, on the other hand, can be heard without a stethoscope if you put your ear close to the chest wall.
However, owners should realize that not all heart murmurs call for immediate follow-up testing to determine their source. For a young kitten with a grade two or lower, an owner might reasonably want to hold off. But as a general rule for adult cats, an echocardiogram, or ultrasound of the heart, is in order. A chest X-ray might be part of a diagnostic work-up, too. And some veterinarians will order a blood test called NT-proBNP, also useful in diagnosing heart disease and assessing the need for further diagnostic tests.
Note that just as not all murmurs are signs of heart disease, lack of a murmur does not automatically mean heart disease is not present. Another way of putting it: Being told your cat has a murmur might be concerning, but it’s better to order tests that will determine whether heart disease is present than to allow an undiagnosed disease to silently progress without being treated. We hope your cat is found to be heart disease-free, or at least only in the early stages of heart disease.
Suzanne Cunningham, DVM, DACVIM
Foster Hospital for Small Animals
College of Veterinary Medicine
At Tufts University