Hypertrophic cardiomyopathy (HCM) is the most common heart disease in cats, affecting an estimated 15-30% of the general cat population. In HCM, the muscular wall of the left ventricle becomes abnormally thickened, reducing the heart's ability to fill with and pump blood efficiently. Some cats with HCM live normal lifespans with no symptoms; others develop life-threatening complications.
Breeds Predisposed to HCM
While HCM occurs in all breeds and mixed-breed cats, certain breeds have a high prevalence of genetic HCM: Maine Coon cats, Ragdolls, British Shorthairs, American Shorthairs, Persians, and Sphynx are among the most affected. Maine Coon and Ragdoll cats can be genetically tested for the mutation that causes HCM in those breeds. Responsible breeders screen their breeding cats annually with echocardiography (heart ultrasound).
Symptoms
Many cats with HCM show no obvious symptoms for years — the first sign may be sudden collapse, difficulty breathing, or paralysis of the hind legs. The latter is caused by a blood clot called aortic thromboembolism that forms in the heart and lodges at the base of the aorta, blocking blood flow to the back legs. This is a medical emergency. Any cat with known HCM who shows labored breathing, open-mouth breathing, or sudden weakness or paralysis of the back legs needs immediate veterinary care.
Diagnosis and Monitoring
HCM is diagnosed via echocardiography — an ultrasound of the heart — performed by a veterinarian with specialized training. X-rays and EKG can provide supporting information. Once diagnosed, cats are typically started on medication to help the heart relax and fill more effectively, and to reduce the risk of clot formation. Regular monitoring with echocardiography every 6 to 12 months tracks disease progression.