The electrical system of the heart is made up of several parts that communicate with one another to signal the heart muscle fibers to contract. The sinoatrial (SA) node located in the right atrium initiates the electrical impulse. The SA node is the natural pacemaker of the heart. The electrical impulse spreads over the atrial muscles causing atrial contraction and then on to the atrioventricular (AV) node. From the AV node the impulse is conducted to the ventricular muscles through the bundle of His, which branches into Bundle Branches that run right and left between the ventricles causing the ventricles to contract. This flow of electrical signals produces a normal heartbeat.