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

Blood pressure in the mammalian aorta is maximum during:

In humans, blood passes from the post caval to the diastolic right atrium of heart due to:

1. pushing open of the venous valves

2. suction pull

3. stimulation of the sino auricular node

4. pressure difference between the caval and atrium