Blood flows from the lungs, where it picks up oxygen, and into the heart through the mitral valve.
When it opens, the mitral valve allows blood to flow into the heart's main pumping chamber called the left ventricle. It has two flaps, or leaflets. The mitral valve is highlighted on this illustration of a heart. Blood flows from the lungs, where it picks up oxygen, and into the heart through the mitral valve. Surgery may be necessary when the valve opens or closes incompletely.