Dermatomyositis is a disease of unknown etiology characterized by inflammation and degeneration of skeletal muscles and cutaneous abnormalities. Cardiac involvement in dermatomyositis-polymyositis is thought to be rare. In recent year, however, there has been an increasing number of reports on cardiac abnormalities in adult dermatomyositis and polymyositis due to development of noninvasive diagnostic techniques. Categorically, these abnormalities have included electrocardiographic changes, cardiac arrhythmias, congestive heart failure, coronary artery disease, and pericarditis. A 56-year-old woman was admittied to the Ewha womans University Hospital with dyspnea and palpitation. She was diagnosed as having dermatomyositis and followed up our department of Dermatology. Electrocardiogram showed a paroxysmal supraventricular tachycardia at as rate of 195/min. The patient was treated with 240mg/day verapamil p.o, 60mg/day prednisone p.o, there was marked improvement of symptoms. Systematic study of cardiac function utilizing echocardiography, Holter monitoring, thallium-201-scan, and gated blood pool studies were conducted in five newly diagnosed patients with dematomyositis-polymyositis. A significant elevation of serum CPK-MB is indicative of cardiac involvement. Cardiac involvement is a serious prognostic sign. We report a case with the review of the literature.