Source: Cardiac Conduction System; Creative Commons: http://commons.wikimedia.org/wiki/File:RLS_12blauLeg.png EKG; Public Domain: http://en.wikipedia.org/wiki/File:SinusRhythmLabels.svg
A system of specialized cells and nodes in the heart that rhythmically pace the heart and time when the chambers contract. Its major components are the sinoatrial node (SA node), atrioventricular node (AV node), bundle branches, and Purkinje fibers.
The SA node is known as the pacemaker of the heart due to its ability to depolarize and repolarize faster than the rest of the cardiac conduction system. It is located in the right atrium of the heart.
Known as the “gateway” between the atria and ventricles; the AV node slows down the rate at which the action potential travels from the atria to the ventricles allowing for more filling time.