A cat’s heart is hardly bigger than a golf ball, compared to our fist-sized blood-pumping organ. But the heart of a cat and the heart of a person work the same way. Thus, for either species, a heart murmur means blood is swishing around to some degree rather than flowing as efficiently as it should (or even flowing in the wrong direction). But here’s the difference.
For a person, how loud and insistent a murmur sounds when the doctor listens with a stethoscope gives an indication of the degree to which the heart is compromised. That’s not necessarily true for a cat.
Confused? So are many others. Heart murmurs in cats are common, occurring in an estimated one out of three pets. Herein, your feline heart murmur questions, answered.
How are heart murmurs rated?
The murmurs of both cats and people are rated on a scale of 1 to 6. If a person’s murmur is a quiet 1, it’s something to watch over time to see if it worsens but probably not something to treat. A cat, on the other hand, may have a grade 1 murmur and have significant heart disease — even if he doesn’t seem sick. And sometimes a feline murmur doesn’t indicate disease at all, while other times it might be a sign of a condition unrelated to heart health.
If the veterinarian hears a heart murmur in my cat, what happens next?
Because identifying a murmur in itself doesn’t diagnose disease in a cat, typically your vet will go on to suggest an echocardiogram, which is an ultrasound of the heart that shows how blood is flowing in that organ in real time. That’s the best way to tell if your cat has serious heart disease or perhaps a benign condition. It will help determine the cause of the murmur and also whether blood is flowing backward and leading to fluid buildup in the lungs or chest cavity. Sometimes an X-ray and diagnostic blood testing is ordered as well.
What causes a heart murmur in a cat besides heart disease?
A number of kittens are born with soft, “innocent” heart murmurs with a 
grade 1 or 2 that they simply outgrow before they reach adulthood. Most often, a vet will not even order an echocardiogram in such cases but will take a wait-and-see approach. A heart murmur in a cat can also be indicative of conditions that include (but are not limited to) anemia, infection, obesity, and emaciation.
If heart disease is found, is there effective treatment?
The prognosis depends largely on how far along the heart disease is by the time the veterinarian sees the cat. But often, with appropriate treatment, a cat can live a long time — maybe years, with good quality of life. Once the root cause of the condition has been determined, medications can be prescribed to slow a cat’s heart rate, decrease the heart’s need for oxygen, reduce demands on the heart’s lower chambers (the ventricles), help the heart muscle to relax, or inhibit the formation of blood clots. Dietary measures, such as limiting salt, can help, too, since salt retains fluid and much of the aim is to keep excess fluid away from the lungs and chest. There’s truly a lot that can be done.
The anatomy of a murmur
In most cats with heart disease, a murmur is caused by a structural abnormality called cardiomyopathy that leads the heart to become misshapen in some way. The heart muscle grows too thick — or stretches and becomes too thin. That makes the blood-pumping mechanics of the heart go awry, with the results ranging from respiratory distress to blood clots that cause paralysis to congestive heart failure resulting from the aforementioned fluid buildup. In rare cases, sudden death can occur.
The most common type of cardiomyopathy by far is hypertrophic cardiomyopathy. It means there’s thickening of the ventricles, the heart’s larger chambers. That compromises blood flow because it interferes with the heart’s pumping action.
This particular form of feline heart disease leads to congestive heart failure. Fortunately, many of the drugs that have been developed to treat heart disease specifically combat the fluid accumulation and effects of hypertrophic cardiomyopathy. They let a cat live comfortably for quite a while even though the disease can’t be cured.
