cardiac cycle [Gk, kardia + kyklos, circle] , the cycle of events in the heart during which an electrical impulse is conducted from the sinus node to the atrioventricular (AV) node, to the AV bundle, to the bundle branches, and to the Purkinje fibers, causing depolarization of the atria followed by depolarization of the ventricles. Depolarization leads to contraction. The contractions of the left and the right atria are nearly simultaneous; they precede the nearly simultaneous contractions of the ventricles. Structural, chemical, or electrical abnormalities may cause a large variety of anomalies in the cardiac cycle.
