Cardiac involvement in polymyositis is more prevalent than previously assumed. A 59-year-old and a 58-year-old man presented with cardiac involvement preceding skeletal muscular lesions, admitted because of increased levels of muscle-derived enzymes and left ventricular dysfunction with ECG abnormalities. Coronary angiography revealed no stenotic lesions. Right ventricular endomyocardial biopsy disclosed myocarditis. Left ventriculography showed local asynergy of cardiac wall motion. After admission the weakness and atrophy of skeletal muscles progressed gradually and high levels of muscle-derived enzymes persisted. Electromyography and skeletal muscle biopsy confirmed the clinical diagnosis of polymyositis. Both patients were diagnosed as having polymyositis with cardiac involvement, and treatment with steroids was started. Symptoms improved significantly, and the CK enzyme level was reduced effectively. The condition of one patient was well controlled, but the other suffered from repeated heart failure due to severe left ventricular dysfunction. The clinical spectrum of polymyositis is wide and variable. Further studies are needed to evaluate the detection, management, and prognosis of the disease as well as the pathogenesis and to prevent progression of cardiac involvement.