Which structure in the heart initiates normal sinus rhythm?

The sinoatrial node is the primary pace-setting structure in the heart, responsible for initiating the normal sinus rhythm. Located in the right atrium near the entrance of the superior vena cava, it generates electrical impulses that spread through the atrial walls, leading to their contraction and the subsequent movement of blood into the ventricles. This activity establishes the heart rate and rhythm, ensuring coordinated pumping throughout the heart chambers.

The normal sinus rhythm refers to the heart operating under the control of the sinoatrial node, thus highlighting its essential role as the natural pacemaker. The regular electrical signals produced by this node dictate not only the rhythm of the heart but also contribute to the synchronization of heartbeats, allowing the heart to function effectively under varying physiological conditions.