Which statement best describes the roles of the SA and AV nodes in the heart?

• A. The SA node acts as the natural pacemaker, while the AV node helps coordinate the timing of heart contractions
• B. The AV node acts as the natural pacemaker, while the SA node helps coordinate the timing
• C. The SA node coordinates the timing of contractions; the AV node is the pacemaker
• D. Both SA and AV nodes act as pacemakers

Answer: (A)

The key idea is how the heart’s electrical system paces itself and times its contractions. The sinoatrial (SA) node in the right atrium automatically generates impulses, setting the heart’s natural pace. That makes it the natural pacemaker, typically driving the heartbeat at about 60–100 beats per minute in a resting adult.

From there, the impulse travels to the atrioventricular (AV) node, which sits at the border between the atria and ventricles. The AV node introduces a brief delay, allowing the atria to finish contracting and push blood into the ventricles before the ventricles are stimulated to contract. This delay coordinates the timing of atrial and ventricular rhythms so the heart works efficiently.

The AV node isn’t the primary pacemaker under normal conditions; it mainly coordinates timing and can take over as a slower backup pacemaker only if the SA node fails. So the statement that the SA node is the natural pacemaker and the AV node coordinates timing best captures their roles.