Undifferentiated pleomorphic sarcoma, also called malignant fibrous histiocytoma (MFH), is a very rare malignancy of the heart and has a poor prognosis. We describe a case in a 59 year old man with an accidental finding of a left atrial mass on echocardiography performed after percutaneous coronary intervention. Histopathological and immunohistochemical examination of the mass after surgical resection established a rare diagnosis of MFH. There was no metastasis and the patient underwent chemotherapy. We show our fi ndings on transesophageal echocardiography, histopathology, and immunohistochemistry.