When coronary arteries are significantly blocked (>70% stenosis), pain symptoms often occur with exercise in the form of stable angina, or at rest in the form of unstable angina.
Bypass vessels are harvested as free grafts from the saphenous veins of the legs. These are anastomosed to the aorta and then to the coronary arteries, literally bypassing the blocked regions.
The internal mammary arteries, which lie on either side of the sternum within the rib cage, can also be harvested and anastomosed directly to the coronary arteries. These grafts are less likely to stenose than are vein grafts.
The procedure can be performed either on or off cardiopulmonary bypass.