Coronary artery bypass graft surgery (CABG) involves sewing one end an artery or vein above a blocked coronary artery and the other end below the blockage, thereby allowing blood an alternative means to get to the heart. The arteries or veins used for the bypass (which are known as "grafts") are usually obtained from the leg or the chest wall. Bypass surgery may not be possible if the coronary artery is heavily calcified or if the disease is very widespread. CABG can be done with or without connecting the patient to heart-lung machine, depending on the kind of blockages and surgeon's decision.

Several new surgical approaches are being developed, which can potentially reduce the discomfort and complications associated with traditional bypass surgery. These are collectively referred to as being "minimally invasive." In general, these approaches focus on performing bypass surgery though a very small chest incision and performing bypass surgery while the heart is still beating (ie, without the need for a heart/lung bypass machine).

is bypass surgery done through a small cut (incision) in the lower part of the sternum (chest bone) only, rather than full cut across it. This type of surgery, which is possible in selected cases only, is associated with a small scar, lesser pain and faster recovery. Alternatively, this surgery can also be done through a small cut on the left side of the chest.

The location and degree of coronary artery blockages are determined before surgery by using a procedure called heart catheterization, or coronary angiogram. This procedure provides an outline, like a road map, of the arteries of the heart.

Bypass surgery is often recommended over angioplasty when the left main coronary artery is narrowed by more than 50 percent, when angioplasty does not relieve angina, when many arteries are narrowed, or when the heart's left ventricular pumping function is substantially impaired. Bypass surgery is also preferred over angioplasty in diabetic patients who have two or three vessels involved.

Bypass surgery can very effectively relieve angina and can even prolong life in people with severe coronary heart disease, such as those with three-vessel involvement associated with impaired left ventricular pumping function. However, the success of bypass surgery on symptoms and on survival depends upon several factors, including the pattern and extent of arterial narrowing, the general progression of coronary heart disease over time, and the blood vessels used for bypass. In general, bypass surgery is more likely than angioplasty to provide complete revascularisation.

About 95 percent of people who have narrowing of several arteries have improvement or complete relief of their angina immediately after surgery. About 85 to 90 percent of people remain angina-free at one to three years after surgery, and about 75 percent of people remain angina-free or free of major coronary events at five years after surgery. By 10 years, about one-half of all grafted vessels become narrowed or occluded, and by 15 years, about 85 percent of grafted vessels become narrowed or occluded. These late events usually require a second surgery