A 57-year-old man was referred to our hospital due to dyspnea on exertion with severe mitral regurgitation. Because he had underdone right pneumonectomy 37 years earlier due to congenital defect of the right pulmonary artery, his mediastinum was severely shifted to the right, and his pulmonary function was poor. Mitral valve repair was successfully performed with right thoracotomy approach, which made excellent exposure of the mitral valve. The patient was extubated three hours after the surgery. He was discharged on the 30th postoperative day without postoperative respiratory complications. With an appropriate plan of the surgery and postoperative optimal management, cardiac surgery can be performed on patients with a single lung.