Overview Hypertrophic cardiomyopathy (HCM) is a disease in which the heart muscle becomes thickened (hypertrophied). The thickened heart muscle can make it harder for the heart to pump blood. Hypertrophic cardiomyopathy often goes undiagnosed because many people with the disease have few, if any, symptoms. However, in a small number of people with HCM, the thickened heart muscle can cause shortness of breath, chest pain or changes in the heart's electrical system, resulting in life-threatening irregular heart rhythms (arrhythmias) or sudden death. Signs, Symptoms and Risks Some people with hypertrophic cardiomyopathy don’t have symptoms while others may only feel symptoms with exercise or exertion. Some people may not have signs or symptoms in the early stages of the disease but may develop them over time. Knowing the signs and symptoms of HCM is important. It can help with getting an early diagnosis when treatment may be most effective. Signs and symptoms of HCM include: Chest pa...