What is the firing rate of the Bundle of His?

• A. 60-80 BPM
• B. 20-40 BPM
• C. 40-60 BPM
• D. 70-90 BPM

Answer: (C)

Understanding the intrinsic firing rates of the heart’s conduction system helps explain this. The heart’s natural pacemaker is the SA node, which fires about 60–100 times per minute. If the SA node slows or fails, the next backup pacemaker is typically the AV node, which paces the ventricles around 40–60 bpm. The Bundle of His sits between the AV node and the Purkinje fibers; it can take over as a slower pacemaker in the same general range, about 40–60 bpm, providing a safe, steady ventricular rhythm when higher centers aren’t driving the heart. The Purkinje system behind it tends to be slower, around 20–40 bpm, if both SA and AV nodes fail.

So the firing rate of the Bundle of His is best described as 40–60 bpm. Rates above that (like 60–100) reflect the SA node’s rhythm, and rates as low as 20–40 bpm reflect Purkinje/ventricular escape rhythms.