During ventricular systole the atrioventricular valves
- A. close, preventing blood from flowing back into the atria
- B. open fully to let blood into the ventricles
- C. dissolve under pressure
- D. contract actively like muscle
Explanation
Rising ventricular pressure lifts the flaps of the tricuspid and bicuspid valves shut, and chordae tendineae anchored to papillary muscles stop them turning inside out. Their closure is the first heart sound.