lves produce the heart beat sounds. When the heart beats, the valves close to keep the blood form flowing backwards. The heart beats more than one hundred thousand times per day. The valves must be able to flex, stretch and hold back pressure hundreds of million times in an average lifetime. The mitral and aortic valves are on the left side of the heart. These are most commonly affected by aging because the pressure is higher on this side. The right heart valves can be damaged by infection or lung disease. Regardless of the valve damage, as they harden or weaken they do not open properly and therefore blood flow may be blocked. Heart valve conditions may also be congenital. Diseases such as rheumatic fever or bacterial infections may also scar or destroy the valves. Heart valve diseases fall into two categories, stenosis and incompetence. The stenotic heart valve prevents full opening of the valve because of the stiffened valve tissue, therefore the heart works harder to push blood throughout the valve. The incompetent valve cause insufficient blood circulation by permitting backflow of blood on the heart. There are two main types of prosthetic valve designs: mechanical and bioprosthetic (tissue). Mechanical heart valves were first implanted in 1952. Since then, over 30 different mechanical designs have originated. The material used to no cause clotting in the blood stream, however, they do not induce coagulation. Most commonly used materials include: stainless steel alloys, molybdenum alloys, pyrolitic carbon, silicone, teflon, and polyester for sewing rings (Summerscale, 2-4). The advantages of mechanical valves are their high durability. They typically last the lifetime of the patient. The disadvantages include the increase risk of blood clotting, which in turn increases the risk for heart attack or stroke. Therefore, mechanical valve recipients must take an anticoagulant drug chronically, which could make the patient bord...
