Cardiomyopathy

any disease of the heart muscle, leading to decreased function: usually of unknown cause.
Contemporary Examples

Cardiologists discovered Takotsubo cardiomyopathy just a few years ago.
‘Zoobiquity’: What Animals Can Teach Us About Our Health Carl Zimmer June 16, 2012

noun
(pathol) a disease of the heart muscle usually caused by a biochemical defect or a toxin such as alcohol

cardiomyopathy car·di·o·my·op·a·thy (kär’dē-ō-mī-ŏp’ə-thē)
n.
A disease or disorder of the heart muscle, especially of unknown cause. Also called myocardiopathy.
cardiomyopathy
(kär’dē-ō-mī-ŏp’ə-thē)
Any of various structural or functional abnormalities of the cardiac muscle, usually characterized by loss of muscle efficiency and sometimes heart failure. Cardiomyopathy can result from numerous causes, including congenital defects, acute or chronic infections, coronary artery disease, drugs and toxins, metabolic disorders, connective tissue disorders, or nutritional deficiencies. In some patients, the cause is unknown.