The human body has a group of cells at the top of the right atrium called the sinus node. Under normal conditions, the sinus node controls the delivery of each electrical impulse and is a natural pacemaker, the “command” of the heart. The electrical impulses from the sinus node are transmitted from the atria to the ventricles, causing the ventricles to contract and produce a heartbeat; each ventricular contraction is a true heartbeat. On the way from the atria to the ventricles, the electrical impulses pass through a “staging area” called the atrioventricular node. Too fast a ventricular beat can lead to heart failure and even fatal consequences. The atrioventricular node has an innate protective effect by filtering out too fast electrical impulses, thus preventing the atria or sinoatrial node from sending too fast electrical impulses down to the ventricles. After passing through the AV node, the electrical impulses are conducted along the bundle of Hirschsprung’s bundle, to the bundle branches, and then to a “grid” of structures that are widely distributed in the myocardium, which excite the ventricular muscle and cause the heart to beat.