Cardiac sarcoidosis induces heart failure death or sudden death in many cases and is thus often associated with a poor prognosis. In Japan 47-78% of sarcoidosis patients die of cardiac lesions. Early diagnosis is important in such cases, and a comprehensive judgment based on the endomyocardial biopsy, echocardiography and nuclear medicine examination findings should be made according to the 'Handbook of the Diagnosis of Cardiac Sarcoidosis'. Once a diagnosis is made the introduction of steroid therapy should be considered. Steroid administration should be conducted referring to the 'Guidelines to the Treatment of Cardiac Sarcoidosis'.