Heart bypass surgery begins with an incision made in the chest, with the breastbone cut exposing the heart. Next, a portion of the saphenous vein is harvested from the inside of the leg. Pieces of this great vein will be used to bypass the blocked arteries in the heart. The venous graft is sewn to the aorta and to the affected coronary artery past the blocked site. The internal mammary artery from the chest may also be used to bypass a clogged artery. Several arteries may be bypassed depending on the condition of the heart.

Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") surgery, and colloquially heart bypass or bypass surgery, is a surgical procedure consisting of either diverting the left internal thoracic artery (left internal mammary artery or "LIMA") to the left anterior descending (LAD) branch of the left main coronary artery; or a harvested great saphenous vein of the leg, attaching the proximal end to the aorta or one of its major branches, and the distal end to immediately beyond a partially obstructed coronary artery (the "target vessel") - usually a 50% to 99% obstruction.

Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage") surgery, and colloquially heart bypass or bypass surgery, is a surgical procedure to restore normal blood flow to an obstructed coronary artery. A normal coronary artery transports blood to and from the heart muscle itself, not through the main circulatory system.

There are two main approaches. In one, the left internal thoracic artery (internal mammary artery) is diverted to the left anterior descending branch of the left coronary artery. In the other, a great saphenous vein is removed from a leg; one end is attached to the aorta or one of its major branches, and the other end is attached to the obstructed artery immediately after the obstruction to restore blood flow.

CABG is performed to relieve angina unsatisfactorily controlled by maximum tolerated anti-ischemic medication, prevent or relieve left ventricular dysfunction, and/or reduce the risk of death. CABG does not prevent myocardial infarction (heart attack). This surgery is usually performed with the heart stopped, necessitating the usage of cardiopulmonary bypass. However, two alternative techniques are also available, allowing CABG to be performed on a beating heart either without using the cardiopulmonary bypass, a procedure referred to as "off-pump" surgery, or performing beating surgery using partial assistance of the cardiopulmonary bypass, a procedure referred to as "on-pump beating" surgery. The latter procedure offers the advantages of the on-pump stopped and off-pump while minimizing their respective side-effects.

CABG is often indicated when coronary arteries have a 50 percent to 99 percent obstruction. The obstruction being bypassed is typically due to arteriosclerosis, atherosclerosis, or both. Arteriosclerosis is characterized by thickening, loss of elasticity, and calcification of the arterial wall, most often resulting in a generalized narrowing in the affected coronary artery. Atherosclerosis is characterized by yellowish plaques of cholesterol, lipids, and cellular debris deposited into the inner layer of the wall of a large or medium-sized coronary artery, most often resulting in a focal partial obstruction in the affected artery. Either condition can limit blood flow if it causes a cross-sectional narrowing of at least 50 percent.

Procedure: The chest is opened via a median sternotomy and the heart is examined by the surgeon.
The bypass grafts are harvested – frequent vessels are the internal thoracic arteries, radial arteries and saphenous veins. When harvesting is done, the patient is given heparin to inhibit blood clotting.
In the case of "off-pump" surgery, the surgeon places devices to stabilize the heart.
In the case of "on-pump" surgery, the surgeon sutures cannulae into the heart and instructs the perfusionist to start cardiopulmonary bypass (CPB). Once CPB is established, there are two technical approaches: either the surgeon places the aortic cross-clamp across the aorta and instructs the perfusionist to deliver cardioplegia with a cooled potassium mixture to stop the heart and slow its metabolism or performing bypasses on beating state (on-pump beating).
One end of each vein graft is sewn on to the coronary arteries beyond the obstruction and the other end is attached to the aorta or one of its branches. For the internal thoracic artery, the artery is severed and the proximal intact artery is sewn to the LAD beyond the obstruction.
Protamine is given to reverse the effects of heparin.
Chest tubes are placed in the mediastinal and pleural space to drain blood from around the heart and lungs.
The sternum is wired together and the incisions are sutured closed.
The patient without complications is discharged in four or five days.

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