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A small mass of specialized cardiac muscle fibers located in the posterior wall of the right atrium of the heart that acts as a pacemaker by generating at regular intervals the electric impulses of the heartbeat. Also called sinoauricular node, sinus node.
si′no•a′tri•al node′(ˈsaɪ noʊˈeɪ tri əl, ˌsaɪ-)
a small mass of tissue in the right atrium functioning as pacemaker of the heart by giving rise to the electric impulses that initiate heart contractions.
(or SA node) Special cells in the heart wall, forming its natural pacemaker.