Hypertrophic Cardiomyopathy: Heart Disease in Cats

Hypertrophic cardiomyopathy (HCM) is a disease that causes the heart muscle to abnormally thicken. Although it is the most common heart disease seen in cats, it is relatively rare in the cat population as a whole.

Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from hypertrophic cardiomyopathy or another serious condition, a veterinary specialist is available at an ExpertVet certified or affiliated hospital.



The heart of your cat has four chambers: two upper chambers and two lower chambers. The thickening caused by hypertrophic cardiomyopathy primarily affects the left ventricle of the heart and does so in a variety of patterns. The left side of the heart is responsible for pumping oxygenated blood from the lungs out into the tissues of the body through the arteries. If the left side grows too thick, it scars and becomes stiff, thus weakening your cat’s ability to pump blood.

Many cats with HCM are only mildly affected and never experience clinical problems with the disease. However, some cats experience a slow progression of heart disease over time. Unfortunately, it is impossible to tell which type of disease an individual cat has. As the disease progresses, scar tissue replaces the thickened ventricle muscle, which eventually becomes very stiff as well as too thick. This causes the filling pressure of the left ventricle to rise. Imagine pouring water into a thick and thin-walled balloon. The thinner-walled balloon is easily expandable and would fill readily. In order to fill the thick-walled balloon, the water pressure would need to be higher in order to fill. This thick-walled balloon is comparable to a stiff left ventricle. This elevated pressure within the heart has three potential outcomes:

1. Congestive Heart Failure (CHF): the most common outcome in cats with severe HCM; it can happen if the pressure is high enough to cause fluid to leak into the lungs.

2. Clot formation: an enlarged left chamber is unfortunately an ideal location for a blood clot to form. Once formed, it is often released into the bloodstream and lodges in the blood supply to the hind legs causing acute hind limb paralysis.

3. Sudden death: this is a RARE but possible outcome.