Which node initiates the normal heartbeat?

Which node initiates the normal heartbeat?

• A. SA node
• B. AV node
• C. Bundle of His
• D. Purkinje fibers

Answer: (A)

The heart’s rhythm is set by the natural pacemaker with the highest automaticity. The Sinoatrial (SA) node sits in the right atrium and fires spontaneously at the fastest rate, so it starts each heartbeat. When it triggers, the impulse rapidly spreads through the atrial muscle, causing atrial contraction and the P wave on the ECG. It then reaches the atrioventricular (AV) node, which provides a brief delay to allow the ventricles to fill, before the impulse travels down the His-Purkinje system to activate the ventricles and produce the QRS complex.

The other nodes can take over if the SA node fails, but they do so at slower intrinsic rates, which is why they’re not the normal initiators of the heartbeat.