Answer: The atria empty into ventricles before ventricles contract.
- A The ventricles contract before the atria
- B The atria empty into ventricles before ventricles contract
- C The valves stay permanently closed
- D The heart rate slows to zero
Correct answer: B. The atria empty into ventricles before ventricles contract
Explanation: The delay at the AV node allows the atria to complete their contraction and fill the ventricles before ventricular contraction begins.
A single ECG cycle: the P wave marks atrial depolarisation (contraction signal), the large QRS complex marks ventricular depolarisation, and the T wave marks ventricular repolarisation (recovery) before the next cycle begins.
Concept context
Blood, lymph, the heart, the cardiac cycle, blood pressure, and ECG. High NEET weightage.