Hypertrophic Cardiomyopathy (HCM): is a cat disease where the heart muscle progressively becomes thicker. As a result, the heart muscle becomes stiff and has difficulty to relax, and the blood encounters difficulty to pass through the heart itself and remains cumulated into the left atrium and the lungs. Cats start to breathe more heavily and are at risk of thromboembolization. It is very important to act promptly and discover the presence of the disease on time with the use of cardiac ultrasound. Treatment is always medical.