The atrioventricular valves open and shut passively in response to pressure differences in the heart chambers.
The atrioventricular (AV) valves are located between the atria and the ventricles of the heart.
As blood returns to the atria and the atria contract, the increased pressure on the AV valves forces them to open.
Then the ventricle contracts to push the blood out of the heart into an artery.
Since the ventricular pressure is greater than the atrial pressure, it presses the cusps of the AV valve together until their edges meet, closing the valve.