A 36-year-old man suffering from exertional dyspnea was admitted to our hospital. An echocardiogram showed a left atrial tumor, which was excised via the left atrial approach. Histological examination of the surgical specimen revealed that it was a myxosarcoma. Twelve months after the surgery, the tumor recurred in the left atrium, and metastatic tumors were found in the right atrium and right ventricle. Surgery was performed once again, but examinations 5 months after the second surgery showed local recurrences and multiple metastases. Although the patient had received chemotherapy, he died 30 months after the first operation.