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. | |
Atria contract. Ventricles fill with more blood. Contraction reaches AV node. |
