Pressure and volume changes and associated valve movements during the cardiac cycle. Candidates should be able to analyse and interpret data relating to pressure and volume changes during the cardiac cycle.

Diastole

The ventricle relaxes, decreasing its pressure. This causes the blood which it just pushed into the aorta/pulmonary (left/right) flow back towards the heart trying to get to the low pressure area: the blood pushes the semi-lunar valve shut (making the second noise of a heart beat 'dub')

Blood flows from the atrium into the ventrical. This happens because there is a lower pressure in it: 1. because it has no blood in and 2. because it has just relaxed.
The blood going through pushes the atrio-ventricular valves open.

Atrial systole

The atrium contracts: so there is more pressure on the blood. It does this to push the remaining blood into the ventricle that didn't flow in during diastole.

Ventricular systole

Ventricles contract- more pressure- pushing blood through the semi-lunar valves, out of the heart.
When they contract the blood pushes against the atrio-ventricular valve, which pushes it shut (this makes the first sound of a heart beat 'lub')

http://library.med.utah.edu/kw/pharm/hyper_heart1.html

Atrium (left):
Bump- atrium contracts.
Drop- blood is pushed into ventricle.
Gradual rise- blood fills the atrium.
Drop- blood flows into ventricle.
Gradual rise- blood continues to flow in and through into the ventricle.

Ventricle (left) pressure:
First small bump- blood is pushed in by atrium.
Massive bump- the ventricle contracts.
Fall with aorta line- blood has been pushed out.
Fall after the aorta line- ventricle relaxes.
Gradual rise- pressure is below that in the atrium so blood rushes in.

When the ventricle pressure rises above that in the atrium, the atrio-ventricular valve is pushed shut.
When the ventricle pressure falls below that of the atrium, the atrio-ventricular valve opens.

Ventricle (left) volume:
Initial rise- blood is pushed in from the atrium.
Fall- blood is pushed out into the aorta.
Plateau- both valves are closed so no blood is moving in or out (volume can't change.)
Increase- blood flows in from the atrium.


Aorta:
When the pressure of the ventricle meets that of the aorta the semi-lunar valve opens.
Big bump- blood is pushed in from the ventricle.
The ventricle pressure drops below that of the atrium, back flow shuts the semi-lunar valve.
Small bump- the elasticity of the walls brings them in before...
Gradual fall- the walls of the aorta relax.

Valves are pushed open because the pressure has been made grater in one chamber than it is on the other side of the valve, so blood tries to go through it into a lower pressure area, pushing it open.