The cardiac cycle is the sequence of events that occur when the heart beats. There are two phases of this cycle:
Semilunar valves close.
Atrioventricular valves open.
Ventricles fill with blood.
Semilunar valves are closed.
Atrioventricular valves are open.
Ventricles continue to fill with blood.
Ventricles fill with more blood.
Contraction reaches AV node.