A comparative illustration of a normal heart and a heart affected by dilated cardiomyopathy. Dilated cardiomyopathy is the most common type of cardiomyopathy often caused by coronary heart disease, diabetes, alcohol abuse, viral infections, thyroid disease, or genetics. The walls of the ventricles stretch and thin (dilate), creating an enlarged heart. This inhibits the heart’s ability to pump enough blood throughout the body and may also result in abnormal heart beats (arrhythmia).