What happens during bypass surgery?

A piece of blood vessel is taken from somewhere else in the body and then reattached below the narrowed or blocked section of the diseased coronary artery. The earliest techniques used the saphenous veins found along the inside of the legs. Then, surgeons began using the internal mammary artery behind the left ribcage. The left internal mammary still is used more than 95 percent of the time because the mammary artery already is attached to a large artery on one end, leaving only one end of the artery to be detached and then grafted to a coronary artery.