Purkinje fibers serve as the final backup pacemaker to the SA node.

• A. True
• B. False
• C. They are the primary pacemaker
• D. They do not participate in conduction

Answer: (A)

Pacemaking in the heart follows a hierarchy. The SA node sets the pace first, and if it fails, the AV node can take over as the next pacemaker. If both of these fail or conduction to the ventricles is blocked, the Purkinje fiber network within the ventricles can generate impulses on its own, driving the ventricles at a slow intrinsic rate (about 20–40 beats per minute). This makes Purkinje fibers the final backup pacemaker when higher-level pacemakers fail, ensuring there is at least a ventricular rhythm, even though it is slow. They are not the primary pacemaker and their automaticity becomes evident mainly in escape rhythms during complete heart block or severe sinus/AV node dysfunction. So the statement is true.