Left ventricular hypertrophic cardiomyopathy is a disease in which the heart muscle becomes abnormally thick, making it harder for the heart to pump blood. The disease is often not diagnosed until sudden arrhythmic death occurs. However, in a small number of people with left ventricular hypertrophy, the thickened heart muscle can cause shortness of breath and chest pain on exertion, but has not been properly examined and treated.