Heart surgery. Gloved hands of a surgeon using a specialised saw to cut through the breast bone (sternum) of a patient who is undergoing heart surgery. This procedure is termed a sternotomy. It will be followed by the spreading of the rib cage and the dissection of the soft tissues of the chest cavity to reveal the heart. The patient is undergoing coronary artery bypass surgery, where blood vessels will be grafted onto the heart to bypass blockages in the heart's coronary arteries. These blockages are caused by atherosclerosis, the build-up of cholesterol and fatty materials on the internal lining of the arteries.