The heart's natural pacemaker is located in which node?

• A. AV node
• B. Atria
• C. Sinoatrial node
• D. Purkinje fibers

Answer: (C)

The heart’s natural pacemaker is the sinoatrial node, a small group of specialized cells in the right atrium near where the superior vena cava enters. It fires spontaneously and has the fastest inherent rhythm, so it sets the pace of the heartbeat. From there, the electrical impulse spreads to the atrioventricular node, then through the bundle of His and Purkinje fibers to coordinate ventricular contraction. The AV node can act as a backup pacemaker if the SA node fails, but it conducts more slowly, producing a slower heart rate. Purkinje fibers are part of the ventricular conduction network, not a pacemaker, and the atria themselves are chambers, not nodes.