Malignant fibrous histiocytoma is the most common soft tissue sarcoma of late adult life. The tumor occurs principally in one of the extremities or in the abdominal cavity or retroperitoneum, but very rarely in the heart. We report a case of M.F.H. that arose from the posterior wall of the left atrium. A 50 years old woman was presented with signs and symptoms of severe congestive heart failure. On 2-D echocardiographic exam, a huge mass was found in the left atrium. The mass was excised under open heart surgery. Histologic examination revealed that the tumor was actually a malignant fibrous histiocytoma.