How the Heart Works
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The Heartbeat: The Heart's Electrical System
The heart, unlike most other muscles, has its own pacemaker, which transmits electrical impulses, signaling the heart to beat. The Sinoatrial (SA) node, or "pacemaker" of the heart, is a bundle of muscle fibers located in the right atrium. The electrical impulse, or signal, begins here and travels through the atria, causing them to contract and force blood into the ventricles.
The Atrioventricular (AV) node receives the signal after it has traveled through the atria and serves as an electrical "gateway" between the atria and ventricles. It connects to fibers, which divide into branches along the septum and down the ventricles.
The impulse continues down two bundle branches and stimulates the ventricles to contract. The contraction forces blood into the lungs and the rest of the body. For every impulse that travels this path, the heart beats, or contracts.