The events in the cardiac cycle are listed below, but they are not in the correct sequence: 1. The impulse moves through Purkyne tissue. 2. An excitation wave spreads across the atria. 3. The atrioventricular node delays the impulse for a fraction of a second. 4. The sinoatrial node contracts. 5. The excitation wave moves upwards from the base of the ventricles. 6. The ventricles contract. 7. The atria contract. Which statement describes the sixth event to occur in the cardiac cycle?
- A1
- B3
- C4
- D5