Heart surgery. Surgeon using an air-powered saw to cut through the sternum (breast bone) of a patient before open heart surgery. This procedure is known as a sternotomy. Once completed, the rib cage will be spread open and soft tissue cut through to reach the heart. The patient is undergoing a coronary artery bypass graft, CABG. During the operation, a healthy artery will be grafted onto the blocked coronary artery, re-routing and restoring blood flow to the heart. A blocked coronary artery leads to loss of blood flow to the heart. This causes chest pains (angina) and heart attacks (myocardial infarctions).