The heart's primary pacemaker is the:

The heart's primary pacemaker is the:

• A. Atrioventricular (AV) node.
• B. Sinoatrial (SA) node.
• C. Purkinje fibers.
• D. Bundle of His.

Answer: (B)

The heart’s natural pacemaker is the sinoatrial node because it generates electrical impulses automatically and at the fastest intrinsic rate, setting the pace for the heart. Located in the right atrium near the superior vena cava, the SA node fires to start each heartbeat, and its impulses spread across the atria to trigger atrial contraction. The impulse then reaches the atrioventricular node, which provides a brief delay to allow ventricular filling, and continues down the conduction system through the bundle of His and Purkinje fibers to stimulate the ventricles. If the SA node fails, the AV node can take over as a backup pacing site, but at a slower rate. Purkinje fibers and the bundle of His are important conduction pathways, not primary pacemakers.

The heart’s natural pacemaker is the sinoatrial node because it generates electrical impulses automatically and at the fastest intrinsic rate, setting the pace for the heart. Located in the right atrium near the superior vena cava, the SA node fires to start each heartbeat, and its impulses spread across the atria to trigger atrial contraction. The impulse then reaches the atrioventricular node, which provides a brief delay to allow ventricular filling, and continues down the conduction system through the bundle of His and Purkinje fibers to stimulate the ventricles. If the SA node fails, the AV node can take over as a backup pacing site, but at a slower rate. Purkinje fibers and the bundle of His are important conduction pathways, not primary pacemakers.