Which component acts as the natural pacemaker of the heart?

• A. Bundle of His
• B. Atrioventricular Node
• C. Sinoatrial Node
• D. Purkinje Fibers

Answer: (C)

The heart’s natural pacemaker is the Sinoatrial node because it has the fastest intrinsic firing rate and initiates the electrical impulse that starts each heartbeat. Located in the right atrium near the superior vena cava, its pacemaker cells spontaneously generate impulses, setting the pace for the heart. This impulse then travels to the atrioventricular node, which slows conduction to give the atria time to contract and fill the ventricles, and on through the His-Purkinje system to coordinate ventricular contraction. The AV node, Bundle of His, and Purkinje fibers mainly function as conduction pathways, not the primary initiators of rhythm. When the SA node isn’t functioning, the AV node can take over but at a slower rate, which shows why the SA node is the natural pacemaker.