Illustration of mitral valve prolapse. The arrow indicates the direction of mitral regurgitation, a consequence of mitral valve prolapse. Located in the heart between the left atrium and left ventricle, the mitral valve consists of two flaps, that open and shut in to allow blood to flow in one direction from the atrium to the ventricle. In patients with MVP, the flaps are enlarged Instead of closing evenly, the flaps collapse or bulge into the atrium, allowing small amounts of blood to flow backwards into the atrium. MVP may lead to a condition known as mitral regurgitation where a large amount of blood is leaking backward through the valve. The extra pumping the heart must do to compensate for the back flow of blood can result in the thickening or enlargement of the heart wall. The condition causes fatigue and shortness of breath and is often treated with medication or surgery.