What is coronary artery bypass (CABG)?

During traditional coronary artery bypass surgery (CABG), the surgeon makes an incision down the center of the chest and through the breastbone to gain access to the heart. The heart is temporarily stopped and the patient's blood is shunted into a heart-lung machine, which substitutes for the beating heart and lungs during surgery. Blood vessels from the chest cavity, arm, or legs are used as replacements for the diseased coronary vessel. These donor vessels can be removed safely because other blood vessels can adequately supply the part of the body from which they were taken. Following completion of the grafting procedure, the heart is stimulated electrically to re-establish its beat, the patient is taken off the heart-lung machine, and the incision in the chest is closed.

Coronary artery bypass is a procedure used to reroute the blood supply around a blocked section of a coronary artery. Surgeons remove healthy blood vessels from another part of the body, such as the leg or chest wall. Then the surgeons surgically attach the vessels to the diseased artery in such a way that the blood can flow around the blocked section.

Basically this is surgical plumbing. Imagine you have a sink on the 2nd floor of your house that is not draining because a pipe somewhere between the 2nd floor and the basement is blocked and clogged up. You don't want to tear up the floors and walls to fix the clogged pipe so you attach a new pipe to drain the sink upstairs and reattach it in the basement where the pipe exits to the sewer. You in fact "bypass" the blocked pipe and reroute the water downstream. Sounds easy right? It's slightly more complicated to do this on a human heart but the concept is essentially the same.

Surgeons bypass the blocked coronary arteries with vein or arterial grafts which are hollow tubes like pipes by sewing them to coronary arteries downstream beyond the blockages and get the inflow of blood by attaching them to the aorta upstream. This brings a better flow of blood into the territory of heart muscle that is not being perfused by the blocked coronary arteries. Problem fixed.