Seventy-five primary sarcomas of the heart were classified by histologic appearance as angiosarcoma (26 cases), undifferentiated sarcoma (18 cases), osteosarcoma (9 cases), fibrosarcoma (6 cases), malignant fibrous histiocytoma (6 cases), leiomyosarcoma (4 cases), myxosarcoma (3 cases), synovial sarcoma (2 cases), and neurofibrosarcoma (1 case). The ages of the patients ranged from 1 to 75 years at the time of presentation (mean, 39 years). Angiosarcomas were predominantly right-sided and osteosarcomas left-sided. Forty patients treated surgically were examined, and survival correlated with clinical and histologic parameters. the survival rate was poor, with a mean of 11 months and median of 6 months. By univariate analysis, the survival rate was more favorable for patients with tumors located on the left side of the heart, without necrosis, with a low mitotic count, and without metastasis at diagnosis. Survival rates were better in patients receiving chemotherapy and radiation therapy. Age, gender, presence of differentiation, and histologic type did not affect prognosis. By multivariate analysis, a low level of mitotic activity and any therapy were the only significant factors affecting survival rate. Immunostaining with commercially available antisera was useful in the diagnosis of sarcoma but not in subclassification of 19 tumors so tested. Although the prognosis for patients with cardiac sarcomas is dismal, histologic grading is useful in predicting outcome, as has been shown for soft tissue sarcomas of other sites.