We report a case of an adenomatoid tumor involving the heart. The lesion was found incidentally at the time of cardiac surgery, measured 1.0 cm, and was poorly demarcated from the adjacent myocardium. Microscopically, the tumor consisted of aggregates of relatively large, epithelioid cells that coalesced to form tubular spaces and occasionally branched into anastomosing channels. The neoplastic cells were strongly immunoreactive with antibodies against cytokeratin. The pathologic features of this unusual cardiac tumor are diagnostic of an adenomatoid tumor, a relatively rare benign neoplasm of mesothelial origin usually found in association with the genital tract. Although rare cases of adenomatoid tumors found outside of the genital tract have been described, including two recently reported pleural tumors, it has not been described to involve the heart.