Forty-five cases of cardiac angiosarcomas were reviewed, and the data were compared with those of a 1968 review of 41 other cases which revealed these tumors to be typically located within the right atrium as large symptomatic masses and to be rapidly fatal, with the diagnoses usually determined only at autopsy. The relationship of these tumors to Kaposi's sarcoma was also examined. The findings paralleled those of the previous review. Additionally, the following points emerged: With the aid of newer imaging techniques, localization, biopsy diagnosis and resection of the atrial tumors are now being achieved more often, with some improvement in survival. Like angiosarcomas of other organs, atrial angiosarcomas exhibit highly variable histologic patterns, which often overlap those of Kaposi's sarcoma, and may also present metastatic patterns simulating widespread Kaposi's sarcoma or malignant melanoma. In reported cases of classical, endemic, or epidemic Kaposi's sarcoma, cardiac lesions are uncommon and typically are small, asymptomatic, restricted to the epicardium/or pericardium and, thus, are clearly different, both clinically and pathologically, from the atrial tumor group. The justification for designating cases of the latter group as "primary cardiac Kaposi's sarcoma" is open to debate. A case report illustrates many of the above points.