Cardiovascular surgery is surgery of the heart or great vessels and it is performed by cardiac surgeons. Surgery is done to treat complications of ischemic heart disease (for example, coronary artery bypass grafting), correct congenital heart disease, or treat valvular heart disease from various causes including endocarditis, rheumatic heart disease and atherosclerosis. It also includes heart transplantation. Development of cardiac surgery and cardiopulmonary bypass techniques helped to reduce the mortality rates of these surgeries to relatively low ranks. Coronary artery bypass grafting (CABG) is the most common type of heart surgery. CABG improves blood flow to the heart. Surgeons use CABG to treat people who have severe coronary heart disease (CHD).