Which structure coordinates heart rate by electrically connecting atrial and ventricular chambers?

• A. SA node
• B. AV node
• C. Myocardium
• D. Purkinje fibers

Answer: (B)

The AV node coordinates heart rate by serving as the electrical connection between the atria and the ventricles. It sits at the junction of the atria and ventricles and introduces a deliberate delay to the impulse. That delay gives the atria time to contract and top off the ventricles with blood before they are activated. After this brief pause, the AV node transmits the signal to the bundle of His and then to the Purkinje fibers, which quickly spread the impulse through the ventricles to produce coordinated contraction. The SA node initiates the rhythm but does not link the two chambers directly. Purkinje fibers drive ventricular activation within the ventricles, not the atrioventricular bridge between chambers. The myocardium is the muscle tissue that performs the contraction itself rather than the conduction bridge between chambers.