A patient with a low grade malignant thymoma who also had pleural, pericardial and cardiac invasion with intracardiac extension, presented with signs of superior vena cava obstruction, moderate hepatosplenomegaly and a mediastinal mass on a plain chest radiograph. Radical excision requiring cardiopulmonary bypass for the removal of the intracardiac extension into the right atrium was performed. Despite the patient's failure to receive radiotherapy treatment, he was alive one year after surgery. This case is reported because this mode of presentation of intracardiac extension of a thymoma is uncommon and because only this method of radical excision could ensure near-total removal of the mass and prevent early death from cardiovascular complications.