Benign cardiac tumors are almost uniformly curable, but malignant cardiac tumors are almost always fatal despite of modern techniques of diagnosis and surgical treatment Resection of malignant tumors of heart is occasionally feasible and can result in prolonged survival, although cure is unlikely. Survival may be enhanced by postoperative irradiation in selected patients, but chemotherapy does not appear to be beneficial. Fibromyxosarocoma of the left atrium is a primary malignant tumor of the heart which is extremely rare and has a poor prognosis and rapid recurrence. It is important to differentiate the uniformly fatal fibromyxosarcoma from the more common benign atrial myxoma. A 19-year-old woman with a fibromyxosarcoma of the left atrium which was extirpated surgically, and postoperative irradiation was given[totally 4,500 rads]. She is still alive 9 months postoperatively without recurrence.