The sinoatrial (SA) node is located at the junction of which structures?

• A. Junction of the superior vena cava and right atrium
• B. Along the inferior vena cava opening into the right atrium
• C. In the left atrium near the pulmonary veins
• D. On the posterior wall of the left ventricle

Answer: (A)

The SA node, the heart’s natural pacemaker, sits in the right atrium at the superior junction where the superior vena cava enters the atrium. This location—the high right atrial wall near the SVC opening—puts the impulse origin right at the start of atrial tissue that then rapidly spreads across both atria, coordinating the heartbeat. The other sites described are not where the SA node resides: they are either lower in the right atrium, in the left atrium near the pulmonary veins, or in the left ventricle, which are not involved in initiating the normal atrial pacemaker activity.