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 through 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 of 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 the pressure in the atria the AV valves will close.
AV valves have rate-limiting properties that control the neural excitation received from atria. This is important in reducing the severity of some heart diseases like Wolff-Parkinson-White Syndrome (WPWS). When atria generate an excessive number of action potential, AV valves help to limit the entering of electrical activity to the ventricle, hence reducing the effect of abnormal atrial activity that might affect the ventricles' contraction.