The Conduction System of the Heart

The conduction system of the heart is made up of specialized conducting tissue. Human heart works as an electrically timed pump. The electrical stimulation of the heart originates from SA node (Sinoatrial Node). The location of this node is in the right atrium near the opening of superior venacava. SA node is collection of specialized cells which are capable of producing automatic electrical activity. The SA node is also known as pacemaker of the heart.
The electrical stimulus generated by SA node in the right atrium travels to left atrium. The right and and left atrium  are activated in the first phase of electrical stimulation. As a result both of these chambers contract and pump the blood to right and left ventricle through Tricuspid and Mitral valve.
The electrical signal generated by SA node further travels to AV junction through specialized conducting tissue. The AV junction consists AV node, bundle of his and, right and left bundle branches. The bundle branches are located in the interventricular septum. The right and left bundle branches transmit the electrical stimulus to right and left ventricles respectively with the help of purkinje fibers. These specialized fibers are located in the ventricular myocardium.
Under normal circumstances the SA node serves as the primary pacemaker of the heart. But in some situations if SA node is unable to generate the impulses, the AV node acts as an escape pacemaker.