A 76-year-old woman, suffering from rapidly worsening dyspnea, and general fatigue was referred for evaluation and treatment of cardiac tumor. Echocardiography and computed tomography revealed a large tumor occupying the right atrium and inferior vena cava. We performed partial resection with cardiopulmonary bypass, in order to improve hemodynamics. The pathological examination suggested malignant lymphoma, diffuse large B-cell type. The patient was treated with cyclophosphamide, cyosine, arabinoside, etoposide, dexamethasone and rituximab (CHASER) postoperatively and gained complete response.