MODEL RELEASED. Heart valve surgery. Surgeon's gloved hands lubricating equipment prior to heart valve surgery. During this operation, a balloon catheter will be inflated in the aorta, preventing blood from flowing back onto the valve being operated on. Heart valves prevent the backflow of blood in the heart. Valve failure may be life- threatening. A defective valve can be replaced with a donor or artificial valve. During the operation, the heart must be stopped and its function taken over by a heart-lung machine. Replacement valves can last for several years, and may greatly improve the quality and length of life.