The heart has four chambers. The upper two are the right and left atrium. The lower two are the right and left ventricle. Blood is pumped through the chambers aided by four heart valves. The valves open and close fully to let blood flow in only one direction. The four heart valves are the mitral, tricuspid, pulmonary, and the aortic valve. Each of these valves has a set of flaps, also called leaflets or cusps that open and close completely when blood is pumped through the valves. A heart valve disease is any condition that disrupts the proper function of the valve. When heart valves function properly they open fully to allow blood to flow in a forward direction through the heart and close tightly to prevent blood from flowing backward. Disorders of the heart valve can be alleviated with heart valve surgery. Heart valves can be replaced by tissue (bio-prosthetic) or mechanical (prosthetic) valves. Mechanical valves are designed to have the longest durability and the lowest probability of reoperation; however the main risk is blood clot formation (thromboembolism) and long term anticoagulation (blood thinners). Without it there is a high probability of blood clots to the brain and other organ systems. In 1979, a new mechanical heart valve was introduced. These valves were known as bileaflet valves, and consisted of two semicircular leaflets that pivot on hinges. The carbon leaflets exhibit high strength and excellent biocompatibility. The bileaflet valve constitutes the majority of modern valve designs. These valves are distinguished mainly for providing the closest approximation to central flow achieved in a natural heart valve. A considerable number of patients who require valve replacement and undergo mechanical heart valve implantation sustain cases of thromboembolic complications. This is due to the fact that all currently implanted mechanical heart valves generate pathological flow patterns, which differ significantly from those in the tissue valves. This thrombogenic behavior of mechanical heart valves is primarily due to activation of platelets which have long been regarded as the pre-eminent cells involved in cardioembolism (strokes). To better understand the flow patterns and stresses arising from blood flowing through the mechanical heart valve, particularly the hinge region. A team of researchers and I conduct micro-PIV experiments. The micro-PIV experiments are trying to visualize and quantify what happens to blood cells when they pass through narrow (about 100 microns thick) gaps when the velocity of blood is quite high. PIV systems measure velocity by determining particle displacement over a precisely selected time using a double-pulsed laser technique. So, through our experiments we hope to understand better the blood velocity field as well as the forces that act on cells in the type of situation that occurs in the hinge region.