A 62-year-old man presented with pulmonary adenocarcinoma that penetrated through the pulmonary vein into the left atrium. The tumor in the left atrium was removed via a right lower lobectomy under cardiopulmonary bypass. In selected cases, radical removal of a tumor in patients without mediastinal lymph node involvement may improve the prognosis. The use of cardiopulmonary bypass extends the possibilities of radical tumor removal.