A 40-year-old white male with agnogenic myeloid metaplasia presented to our institution with symptoms of fever, rash and pleuropericardial pain. A two-dimensional echocardiogram revealed a pedunculated left ventricular mass which simulated a left ventricular myxoma. Left ventricular wall motion and coronary arteries were normal on preoperative angiography. The mass was surgically removed and found to be fibrin thrombus. A mild chronic inflammatory infiltrate was present in the base of the thrombus. The formation of thrombus in the left ventricle was ascribed to spontaneous aggregation of platelets and myocarditis of unknown cause.