Heart surgery. Gloved hands of a surgeon using a diathermic cutting tool to cut through the muscle and fat layers in the chest wall of a patient who is undergoing heart surgery. This initial incision will be followed by a sternotomy, where the breast bone (sternum) is split with a special saw. The rib cage is then spread open and the soft tissues of the chest cavity dissected to reveal the heart. Diathermy uses a high-frequency electric current to produce localised heat that can be used to cut through tissue layers with minimal blood loss. The operation involves a coronary artery bypass, where blood vessels will be grafted onto the heart to bypass blockages in the heart's coronary arteries.