Which component of the heart's conduction system is known as the natural pacemaker?

• A. SA Node
• B. AV Node
• C. Purkinje Fibers
• D. Bundle of His

Answer: (A)

Automaticity in cardiac tissue means some cells can generate impulses on their own, and the sinoatrial node has the highest intrinsic firing rate among the conduction pathways. This makes it the natural pacemaker, because it sets the pace for the heart and establishes the normal sinus rhythm. Located in the right atrium near the opening of the superior vena cava, its impulses spread from the atria to the atrioventricular node, then down the Bundle of His and through the Purkinje fibers to activate the ventricles, with the AV node providing a brief delay to allow filling. If the SA node isn’t functioning, other pacemaker regions can take over at slower rates, but the normal, regular rhythm is driven by this primary pacemaker.