Heart surgery. Heart with a grafted mammary artery that has been attached during coronary artery bypass graft (CABG) surgery. This grafted artery (red) is at lower centre. The heart is the large organ seen between the metal rib spreaders. The mammary arteries run either side of the breast bone (sternum). They are particularly suitable for CABG surgery, as they are less susceptible to the clogging processes that block arteries. This one has been isolated (harvested) from the breast bone and attached to the heart in order to bypass a blocked coronary (heart) artery. It already has an arterial blood supply, so only one end needs to be severed and attached to the heart.