To investigate the significance of cardiac damage in the patients with polymyositis (PM)/dermatomyositis (DM)，45 cases of PM/DM in our hospital from 1992 to 1998 were retrospectively analyzed in the aspects of the clinical data，muscle zymogram，X-ray plain films，electrocardiograph，ultrasonic cardiogram. It was found that cardiac damage (51.1 %) occurred in 23 out of 45 cases of PM/DM. Pericardium，cardiac muscle，endocardium and coronary artery were involved. Clinical manifestations were various. Among the cases of cardiac damage，3 died of heart failure. It was indicated that cardiac damage is the most common complication and also one of the common death causes of PM/DM.