Sarcoidosis is a systemic granulomatous inflammation with an unknown cause. The commonly involved sites are the lymph nodes, lungs, skin, eyes, and heart. Although cardiac involvement in sarcoidosis is rarely detected clinically, it is reported in 20-50% of autopsied sarcoidosis patients. Cardiac involvement is one of the most severe conditions of sarcoidosis and may cause sudden death. We report a case of a sudden death due to a massive cardiac sarcoidosis in a 43-year-old man. The microscopic examination revealed an extensive noncaseating granulomatous inflammation in the mediastinal lymph nodes and the heart with no evidence of myocyte necrosis. A special stain and molecular study excluded the possibility of other causes such as fungi or mycobacterium. The authors concluded that the cause of death was attributed to arrhythmia due to a cardiac sarcoidosis with massive involvement of the conduction system.