Cardiac sarcoidosis is a rare but serious condition that affects the heart in patients with systemic sarcoidosis. This study analyzed 84 consecutive autopsied patients with sarcoidosis to determine the incidence and clinical and morphologic manifestations of cardiac sarcoidosis. Of these patients, 23 (27%) had myocardial sarcoidosis. Among these, only four (17%) had grossly evident, widespread myocardial lesions, and all four had sudden, unexpected death. The other 19 patients had microscopically evident granulomatous involvement, with eight (42%) having rhythm or conduction disturbances and three (16%) sudden death. However, none of those who suffered sudden death had a recognized rhythm or conduction disturbance. The study found that although myocardial involvement occurs in at least 25% of patients with sarcoidosis, it most often involves a small portion of the myocardium and is clinically silent. The true incidence of myocardial sarcoid may be even greater than suggested here, as some patients may have small microscopic granulomas that were not identified. Rhythm and conduction disturbances are more common in the cardiac sarcoid group, but the findings suggest that only the small subset of patients with severe, grossly evident myocardial sarcoid are at increased risk for sudden death. The study also found that patients with no cardiac sarcoidosis had a higher incidence of rhythm or conduction disturbances and sudden death. However, these patients were not at greater risk for sudden death than those without cardiac sarcoidosis. The study concluded that the patients at greatest risk for sudden death are those with extensive, grossly evident cardiac sarcoidosis. The presence of a rhythm or conduction disturbance and a defect on thallium-201 myocardial perfusion imaging in the absence of a history of ischemic heart disease may help identify these patients. However, the clinical significance of "mild" cardiac sarcoid remains unclear. The study suggests that arrhythmias appear to be the most predictive of cardiac sarcoid, and that further study with myocardial perfusion imaging may help identify patients at risk for sudden death.Cardiac sarcoidosis is a rare but serious condition that affects the heart in patients with systemic sarcoidosis. This study analyzed 84 consecutive autopsied patients with sarcoidosis to determine the incidence and clinical and morphologic manifestations of cardiac sarcoidosis. Of these patients, 23 (27%) had myocardial sarcoidosis. Among these, only four (17%) had grossly evident, widespread myocardial lesions, and all four had sudden, unexpected death. The other 19 patients had microscopically evident granulomatous involvement, with eight (42%) having rhythm or conduction disturbances and three (16%) sudden death. However, none of those who suffered sudden death had a recognized rhythm or conduction disturbance. The study found that although myocardial involvement occurs in at least 25% of patients with sarcoidosis, it most often involves a small portion of the myocardium and is clinically silent. The true incidence of myocardial sarcoid may be even greater than suggested here, as some patients may have small microscopic granulomas that were not identified. Rhythm and conduction disturbances are more common in the cardiac sarcoid group, but the findings suggest that only the small subset of patients with severe, grossly evident myocardial sarcoid are at increased risk for sudden death. The study also found that patients with no cardiac sarcoidosis had a higher incidence of rhythm or conduction disturbances and sudden death. However, these patients were not at greater risk for sudden death than those without cardiac sarcoidosis. The study concluded that the patients at greatest risk for sudden death are those with extensive, grossly evident cardiac sarcoidosis. The presence of a rhythm or conduction disturbance and a defect on thallium-201 myocardial perfusion imaging in the absence of a history of ischemic heart disease may help identify these patients. However, the clinical significance of "mild" cardiac sarcoid remains unclear. The study suggests that arrhythmias appear to be the most predictive of cardiac sarcoid, and that further study with myocardial perfusion imaging may help identify patients at risk for sudden death.