Chronic expanding hematoma （CEH） after coronary artery bypass grafting （CABG） is extremely rare. We reported a case of successful surgical repair of CEH through lower partial sternotomy approach. The patient was a 73-year-old man who underwent CABG. Fifteen years after the operation, he was admitted to referral hospital because of dyspnea on exertion. Echocardiography and computed tomography revealed a giant intrapericardial mass, which was pressing on the inferior wall of the ventricle. To avoid injury of the aorta and the patent bypass graft in the reentry of the chest, we selected lower partial sternotomy approach. The mass was encapsulated with thick fibrous membrane containing old degenerated coagula and was histopathologically diagnosed as CEH. Postoperative course was uneventful and diastolic heart failure was relieved.