The sinoatrial node (also commonly spelled sinuatrial node, abbreviated SA node or SAN, also called the sinus node) is the impulse-generating (pacemaker) tissue located in the right atrium of the heart, and thus the generator of normal sinus rhythm. It is a group of cells positioned on the wall of the right atrium, near the entrance of the superior vena cava. These cells are specialized cardiomyocytes. Though they possess some contractile filaments, they do not contract robustly.
The SAN was first described in 1907 by Arthur Keith and Martin Flack.
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