Primary cardiac lymphomas diagnosed antemortem are extremely rare. We present a case of primary cardiac lymphma diagnosed antemortem by transvenous biopsy under transesophageal echocardiographic guidance. The patient who was a 62 years old male presented with facial edema, dyspnea on exertion and syncope. The chest X-ray film showed double contour at right cardiac border and the ECG showed marked sinus bradycardia. Transesophageal echocardiography (TEE), chest computed tomography (CT) and magnetic resonance imaging (MRI) showed intracardiac tumor of right atrium, invasing interatrial septum and inlets of superior and inferior vena cava and lateral wall of right atrium. Abdominopelvic CT and bone scan failed to show any extracardiac location. Transvenous biopsy confirmed the diagnosis of malignant lymphoma (diffuse large cell, B cell type). After chemotherapy was begun, the tumor makedly shrunk and symptoms resolved. Primary cardiac lymphoma is extremely rare and almost uniformly fatal, but this case showed that early diagnosis and intensive che-motherapy might contribute to a better prognosis for patients with malignant lymphoma of the heart.