The atrioventricular (av valves are closed while the atria are contracting when the ventricles are in diastole by the movement of blood from atria to ventricles when the ventricles are in systole

The atrioventricular (AV) valves are closed when the ventricles are in systole.
There are two types of atrioventricular valves, and those are the mitral valve, and the tricuspid valve, both of which are located between the upper chambers (atria) of the heart, and its lower chambers (ventricles). Systole refers to the action when the heart contracts, and thus blood is pumped from the chambers into the arteries, and further on throughout the whole body.

Very hard to understand