Coronary bypass surgery is a challenging operation. Essentially, it’s replumbing a patient’s heart, similar to what happens if the gas line to your car's engine gets pinched; in a car shop, the mechanic simply removes the supply line and replaces it with a new one, but for a narrowed coronary artery, a cardiac surgeon will attach a tube and bypass the narrowed artery so that blood can flow around it. Fortunately, many patients have spare vessels in their body which the surgeon can harvest and use as the tube.