Heart surgery. Harvested artery being prepared for use in a coronary artery bypass graft (CABG). The artery is being attached to a special tool that will staple the artery into place. A blood vessel branching off the artery has been tied off with some black thread. During CABG a healthy artery is attached to the diseased coronary artery. This re-routes the blood flow, bypassing the blocked coronary artery. Blood vessels can become blocked by the build up of fatty plaques, atherosclerosis. This reduces blood flow to the areas served by the blood vessel. Inadequate blood flow to the heart can lead to heart pain (angina) or a heart attack (myocardial infarction).