The portion of the atrium in the right side of the heart that is known as the heart's pacemaker is the:
A. atrioventricular bundle
B. sinoatrial (SA) node
C. atrioventricular (AV) node
D. bundle of His
b
Rationale: The sinoatrial (SA) node is a small, elongated mass of specialized cardiac muscle tissue located just beneath the epicardium in the right atrium near the opening of the superior vena cava. It initiates one impulse after another, and be-cause it generates the heart's rhythmic contractions, is known as the pacemaker.
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