Hypertrophic cardiomyopathy (HCM) is the thickening of the heart muscles which makes the heart chambers smaller than normal, causing abnormality in the function of the heart. The primary cause of the disease is genetically based while the secondary may involve conditions like hyperthyroidism and hypertension. Young male cats and certain breeds of dogs such as Maine Coon are at greater risk for developing the disease. In the initial stage of the disease, the animal may not show obvious symptoms. HCM due to secondary causes is common in older cats which includes symptoms like loss of appetite, change in breathing pattern, and behavioral changes. HCM in cats is diagnosed by physical examination, chest X-rays, and ultrasound of the heart. If the disease goes untreated, the result is the stiffening of the muscles to an extent that the heart is unable to pump the blood. Blood clots begin to form in the heart which is showered to the body as the heart pumps the blood. These clots may lodge in the back leg causing pain and paralysis. In most cases, the diagnosis is made after the unexpected death of the cat. Treatment involves therapy for underlying secondary causes of the disease.