Doctors use stethoscope to hear the sounds produced during

Doctors use stethoscope to hear the sounds produced during each cardiac cycle. The second sound is heard when:

1. Ventricular wall vibrate due to gushing in of blood from atria
2. Semilunar valves close down after the blood flows into vessels from ventricles
3. AV node receives signal from SA node
4. AV valves open up

The second sound heard by doctors using stethoscope occurs when semilunar valves close down after the blood flows into vesels from ventricles.