Which statement accurately identifies the pacemaker of the heart?

• A. A The AV node initiates electrical impulses
• B. B The left ventricle initiates impulses
• C. C The sinoatrial node initiates electrical impulses
• D. D The right ventricle initiates impulses

Answer: (C)

The heart’s natural pacemaker is the sinoatrial node, located in the right atrium near the superior vena cava. This small cluster of pacemaker cells has the fastest intrinsic firing rate, typically about 60–100 impulses per minute, so it normally sets the pace for the entire heart. When it fires, the electrical impulse spreads through the atria to trigger atrial contraction, then moves to the atrioventricular (AV) node, which provides a brief delay to ensure the ventricles fill properly before they contract. If the SA node slows or stops, the AV node can take over at a slower rate, and even deeper in the conduction system, ventricular tissue can generate impulses at an even slower pace. The AV node and the ventricles can generate impulses, but they do not serve as the primary initiator of each heartbeat under normal conditions.