Cardiomyopathy is a weakening of the heart muscle which reduces how forceful it can pump. It is often associated with congestive heart failure and arrhythmias. Cardiomyopathy may be caused by alcoholism, heart attacks, heart valve abnormalities, viral infections, high blood pressure, nutritional deficiencies, inflammatory diseases, and after delivering a baby. Cocaine abuse and certain chemotherapy drugs can also cause cardiomyopathy.