Cardiac involvement in polymyositis was investigated in 20 autopsied cases. Clinically, 13 of 18 patients had abnormal electrocardiograms, and 9 of the 20 patients had previous evidence of congestive heart failure. Histologically documented myocarditis was detected in 6 patients (4 with congestive heart failure and 2 without), 4 of whom also had small vessel disease of the myocardium. Patients with polymyositis may have a cardiopathy in the absence of overt myocardial inflammatory disease.