Oxygen is supplied to the heart muscle by the right and the left coronary arteries. These two main arteries further subdivide supplying blood with oxygen to the heart muscle.When these arteries get totally or partially blocked the heart muscle gets insufficient oxygen to perform its work. This initially results in chest pain or angina. If left untreated the heart muscle will actually die. This is called a myocardial infarction or heart attack. With surgical correction a bypass graft is done. That is, a conduit is taken either from the chest or the leg and used to bypass the coronary artery at the point of the blockage
The heart acts like a pump, it generates a pressure, which enables it to pump blood through the lungs and then to the rest of the body. In order to do this the blood must flow only in one direction. The heart accomplishes this because of four one-way valves present inside the heart, which open and close in synergy with each pump of the heart, thereby allowing blood to flow in one direction. If these valves become defective,which could occur as after a valve infection or a heart attack involving the valve, they either become stiff and cannot open which is called stenosis or they may become too flaccid to close which is called incompetence or it may be a combination of both these conditions. When this occurs the pump is unable to generate enough pressure to pump blood throughout the lungs and around the body. During surgery the valve is either repaired or replaced.