Primary leiomyosarcoma of the heart is extremely rare and found in about 0.2% of all cardiac tumors. Here in a 26-year-old man with progressive dyspnea, which had started since 2 months ago, is presented. Echocardiography revealed a left atrial mass, which was suggestive for a atrial myxoma.On the surgery, a tumoral tissue in the left atrium and pulmonary veins with attachment to peripheral soft tissue, was seen and incompletely resected. Histologic examination exhibited a hypercellular,necrotic and mitotically active spindle-celled tumor with fascicular arrangement. Immunohistochemistry showed a positive reaction to SMA in tumoral cells. The patient was advised to refer for postoperative chemotherapy, which was rejected. One year later, the patient was brought to hospital with tumor recurrence. Chemotherapy was initiated for the patient immediately, but the patient was expired 3 days later.