The Atrioventricular valves (AV valves) are located in the heart between the upper Atrium and lower Ventricle chambers. The left AV valve is called the mitral (bicuspid) valve and the right AV valve is called the tricuspid valve. The valves open to allow blood to move throught the heart from the atria to the ventricles, once the atria has emptied the valves will close which will prevent backflow of blood back into the atria and ensure the blood flows in one direction. Blood will initially enter the heart via veins into the atria, the AV valves are closed at this point. When the atria are full with blood and the pressure in the atria exceeds the pressure in the ventricles the AV valves will open. This allows the blood to move from the atria into the ventricles, and when the pressure in the ventricles exceeds pressure in the atria the AV valves will close.