Heart bypass grafts. Coloured coronal computed tomography (CT) scan of the heart of a 72-year-old patient with heart bypass grafts (arrowed, white). These grafts are short lengths of blood vessels that have been grafted onto the surface of the heart (the mass down left and across to lower centre). The chest wall is seen down right in this frontal view. The grafts bypass blockages in the coronary arteries that supply the heart muscle with oxygenated blood, and the operation is called a heart bypass operation. This patient had a triple heart bypass operation, with three grafts made in total. The blockages of the coronary arteries are usually due to a condition such as atherosclerosis, where arteries harden and become blocked by fatty deposits.