Granulocytic sarcoma (GS) is a localized destructive tumor mass composed of immature cells of the granulocytic series, occurring before, concomitantly, or after the overt development of acute or chronic myelogenous leukemia. Although this tumor is known to occur in almost every site of the body, cardiac involvement is rare. We report a case of a 12-year-old female previously treated for 28 months with chemotherapy for acute promyelocytic leukemia, who presented with GS in the left mastoid 3 months after discontinuing treatment. The patient was treated with local radiotherapy only. Thirty months later she presented with heart failure, the result of a right-sided intracardiac mass, while in continuous hematological remission of the primary disease and off therapy. The cardiovascular, hematological, and postmortem findings are described and the literature is reviewed. This is the first clinicopathologic report of GS involving the heart in which the echocardiographic and pathologic findings are detailed.