A 69-year-old man was admitted to our hospital with a complaint of cough and hemoptysis. His chest X-ray showed an obstruction of the right intermediate bronchus and resultant atelectasis of the middle and lower lobes. Cytological examination by bronchoscopy showed squamous cell carcinoma. Although the cancer involvement of the left atrium could not be clearly defined by preoperative chest CT scan, the cancer invasion to the left atrial wall was recognized intraoperatively. Right pneumonectomy along with resection and patch reconstruction of the left atrium, right atrium and atrial septum was performed under extracorporeal circulation. Postoperative hemodynamic state was stable, and echocardiography showed normal volume of the left atrium. Histological examination of the resected specimen showed moderately differentiated squamous cell carcinoma with the involvement of the left and right atrial wall. The resected margins of the left and right atria were free of malignancy. Although he had been clinically in good condition and free from any sign of cancer recurrence, he died of aspiration pneumonia five months after the surgery.