Cardiac involvement in sarcoidosis can be demonstrated in about 25 percent of autopsied cases, but antemortem diagnosis is uncommon. To evaluate the usefulness of the endomyocardial biopsy in detecting cardiac sarcoid disease, the medical records of ten patients with sarcoidosis who underwent endomyocardial biopsy for routine clinical indications were reviewed. The patients fell into two groups: patients with known sarcoidosis and presumed cardiac involvement (n = 8), and patients in whom the biopsy finding of sarcoid disease was unexpected (n = 2). Four patients in the first group had positive endomyocardial biopsy results (granulomas and/or marked mononuclear cell infiltrate) and were treated with glucocorticoid therapy with improvement in three; the fourth was disabled with lung disease. The diagnoses of three other patients were revised on the basis of the biopsy results; their therapy was tailored accordingly. The remaining patient may represent a false-negative biopsy result, based on clinical criteria. The two patients in the second group presented with symptomatic ventricular tachycardia and restrictive cardiomyopathy respectively, and in neither case was sarcoidosis considered prior to biopsy results. Overall, a change in treatment strategy based on biopsy results occurred in eight of ten cases. Thus, endomyocardial biopsy is useful for the diagnosis of cardiac sarcoidosis; treatment strategies may be affected by biopsy findings; and rarely, endomyocardial biopsy can provide the first clinical evidence of sarcoid disease that is otherwise occult.