Autopsy or surgical specimens from six patients with primary cardiac angiosarcoma seen at the Mayo Clinic (all in men) between 1939 and 1988 were studied (patients' ages, 31 to 80 years; mean 50 years). The symptoms were nonspecific and included dyspnea and thoracoabdominal pain in six; anorexia in five; fatigue, hemoptysis, or orthopnea in four; nausea and vomiting, fever, or weight loss in three; and night sweats in two. Cardiomegaly was present in five, and a pericardial effusion or density, a mass adjacent to the heart, or nonspecific ST-T wave changes were present in three. All six neoplasms arose from the right atrium and exhibited epicardial or endocardial extension; three produced obstructive intracavitary right atrial masses. Pulmonary metastatic lesions were noted in five patients. The cardiac neoplasm was diagnosed by computed tomography or magnetic resonance imaging in the three most recent patients, and surgical resection was performed in two of them. Mean survival was 6 months after presentation. Causes of death were pulmonary hemorrhage in three, thoracic metastasis in two, and hemopericardium in one. The diagnosis of primary cardiac angiosarcoma was established at operation in two patients and at autopsy in four. Despite diagnosis by noninvasive imaging procedures and aggressive early surgical intervention, survival was less than 6 months. Thus optimal therapy is unclear.