Which node acts as the pacemaker of the heart, located in the right atrium?

• A. Sinoatrial node
• B. AV node
• C. Bundle of His
• D. Atrioventricular bundle

Answer: (A)

The main concept is that the heart’s natural pacemaker sets the rhythm. The sinoatrial node, located in the right atrium near the entry of the superior vena cava, generates the electrical impulses that initiate each heartbeat. Because it fires at the fastest intrinsic rate (about 60–100 beats per minute in a healthy adult), it dictates the pace of the heart. The impulse then travels to the atrioventricular node, which sits lower in the right atrium near the tricuspid valve and introduces a brief delay to allow the atria to contract before the ventricles beat. After that, the signal moves through the bundle of His and into the ventricles via the Purkinje system. Those pathways conduct the impulse but don’t start it, which is why they’re not the heart’s pacemakers. If the SA node fails, the AV node can take over, but its intrinsic rate is slower, so it’s not the usual pacemaker.