The normal rhythm is called sinus rhythm. Your own natural pacemaker, the sinoatrial (SA) node, is located in the right atrium. At rest, approximately every second, this pacemaker fires and sends an electrical signal through the right and left atria, which contract and empty their blood into the relaxed ventricles. As the electrical signal continues on through a junction, the atrioventricular (AV) node, to the ventricles, the atria relax and the ventricles contract, pumping the blood to the lungs and throughout the body.

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