Primary malignant neoplasms of the heart are very rare disorders, which are found at less 1/1000 necropsies. These malignancies are almost exclusively sarcomas and histologically assume a wide veriety of morphological subtypes, angiosarcomas, rhabdomysarcomas, and fibrosarcomas(or MFH) being the most frequent. We experienced a case in which left atrial myxoma was suspected by 2-D echocardigraphy and the histologic diagnosis of promary MFH was confirmed by operation. A 45-year old woman with primary MFH arising from posterior wall of left atrium, interatrial septum and mitral annulus is presented with a brief view of the literatures. The patient was admitted to our hospital on March 1988, because of exertional dyspnea and intermittent palpitation resction of the masses. To date, more than thirteen months after surgery, the patient is alive and well in state of NYHA class II.