Which anatomical site is identified as the natural pacemaker of the heart?

• A. A Atrioventricular node
• B. B Left ventricle
• C. C Sinoatrial node
• D. D Right ventricle

Answer: (C)

The heart’s natural pacemaker is the Sinoatrial node. Its cells have the highest rate of spontaneous depolarization, so this node initiates the electrical impulse that sets the heart’s rhythm and pace. This impulse starts in the SA node, located in the wall of the right atrium near the superior vena cava, and then travels through the atrioventricular node and onward to coordinate contraction of the atria and ventricles. The AV node can take over if the SA node fails, but its intrinsic rate is slower, so relying on it typically reduces the heart rate. The ventricles themselves do not act as the primary pacemaker; they generate pumping force in response to impulses that originate higher in the conduction system.