Which coordinates ventricular contraction?

• A. SA node
• B. AV node
• C. Atrial tissue
• D. His-Purkinje system

Answer: (D)

Coordinated ventricular contraction depends on rapid, synchronized spread of the electrical impulse through the ventricular conduction pathways. The His-Purkinje system—comprising the bundle of His, bundle branches, and Purkinje fibers—delivers that impulse quickly to both ventricles, causing near-simultaneous depolarization of the ventricular myocardium and a coordinated, strong contraction.

The SA node starts the heartbeat and primarily paces the atria. The AV node delays the signal to allow the ventricles time to fill, but it does not provide the fast, coordinated activation of the ventricles. Atrial tissue can conduct impulses, but it’s not responsible for driving the ventricles in a synchronized way. Hence, the His-Purkinje system is the structure that coordinates ventricular contraction.