Heart contraction begins with the Sinoatrial (SA) node, the hearts pacemaker, firing and sending an electrical impulse to the left and right atriums. This impulse then causes contraction within the atrium and pumps blood to the bottom left and right ventricles. The electrical impulse then is sent to the ventricles through a junction box, called the Atrioventricular (AV) node. The signal is then slowed down to allow time for the ventricles to fill with blood it has received. The impulse then travels to the bundle of His, located in the interventricular septum, then continue to the bundle branches and end in the Purkinje fibers. After the impulse arrives in the Purkinje fibers an impulse tells the right and left ventricle to contract. This contraction
