A 35-year-old woman had underwent an amputation of the right hemimandibula for an osteosarcoma. Twenty months after the operation, she was admitted to our hospital with complaints of syncope. On chest computed tomography and echocardiography, an atrial tumor was disclosed, which extended from the lesion of the left pulmonary lower lobe. This tumor intravascularly developed through the left inferior pulmonary vein. The intracardiac tumor was resected through left atriotomy under cardiopulmonary bypass, and immediately after weaning of bypass left lower lobe was resected. On pathological study the tumor was diagnosed as metastasis of osteosarcoma. Despite postoperative chemotherapy including CDDP, she died of metastasis in pulmonary, adrenal gland and liver 12 months after the second operation.