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SA node which is sinoatrial node, located at the top of the heart’s upper-right chamber (the right atrium). The SA node is sometimes called the heart’s “natural pacemaker.”
The SA node sends electrical impulses at a certain rate, but your heart rate may still change depending on physical demands, stress, or hormonal factors. Sometimes, the SA node does not work properly, causing the heart to beat too fast, too slow, or irregularly. In other cases, the heart’s electrical pathways are blocked, which can also cause an irregular heart rhythm.When an electrical impulse is released from this natural pacemaker, it causes the upper chambers of the heart (the atria) to contract. The signal then passes through the atrioventricular (AV) node. The AV node checks the signal and sends it through the muscle fibers of the lower chambers (the ventricles), causing them to contract.