First, the sternum is cut and the chest opened (a procedure known as "cracking the chest". The heart is usually stopped and the patient is connected to a bypass machine, which takes over the heart's functions for the duration of the operation. Blood vessels are harvested from elsewhere in the body for grafting.
Typically, the saphenous vein from the leg and the left internal mammary artery (LIMA) are used for the bypass. Veins used either have their valves removed or are turned around so that the valves in them do not occlude blood flow in the graft. LIMA grafts are longer-lasting than vein grafts, both because the artery is more robust than a vein and because, being already connected to the aorta, the LIMA need only be grafted at one end. For this reason, the LIMA is usually grafted to the left anterior descending artery (LAD), which supplies the left ventricle, the part of the heart that pumps oxygenated blood around the body. Alternatively, an artery such as the radial artery from the arm, may be used in place of a vein. This is believed to prolong the life of the grafts but this has yet to be proven.
Prognosis following CABG depends on a variety of factors, but successful grafts typically last around 10-15 years.