We experienced four operative cases of lung carcinoma with intra-atrial extension via the pulmonary vein. In two cases, after assessment of the cardiac involvement, we performed extensive surgery under cardiopulmonary bypass. Their postoperative courses were uneventful, and their performance status was improved. However, seven months later one patient died of widespread metastases, while the other is alive but has recurrence. The other two patients underwent ordinary lobectomy because there were no abnormal findings in the hilar examination. However, the lumen of the resected pulmonary vein was filled with tumor tissue. One patient had massive embolism and died on the second postoperative day. The last case had residual tumor dislodging from the left atrium to the aorta. Though he was discharged without any complication, he developed multiple brain metastases 4 months after operation. We conclude that extensive surgery using cardiopulmonary bypass for lung cancer patients with such intracardiac involvement is effective for improvement of PS and reduces the risk of sudden death due to cardiac failure or emboli. Accurate diagnosis of intracardiac extension in these unusual cases is important.