Heart murmurs can be symptoms of a whole lot of things including nothing at all. Some are completely (or nearly so) harmless, others represent more serious heart conditions. They are graded on a 1 to 6 scale, with 1 being mild and 6 being serious.


If it's toward the higher end, the vet may want to run an ultrasound (echocardiogram) to see if there's a problem such as hypertrophic cardiomyopathy (HCM). This is a condition where the heart wall thickens and becomes less compliant so the heart doesn't pump as effectively. HCM is an extremely variable condition. I have two cats with mild HCM who have been treated for about 5 years or so with a once a day pill. Sammy, who died last year at age 19 had very pronounced HCM as well as chronic renal failure. Even so, she lasted 5 years with the condition. And she'd had the heart murmur much longer, and I suspect congenital. (I got her when she was 9, and she had the heart murmur then.)

However, other cats succumb quickly. HCM cats are susceptible to throwing blood clots that can completely block an artery.