Phase 1: Ventricular Filling

During atrial diastole, the ventricles expand and their pressure drops below that of the atria. This causes the atrioventricular valves to open; blood flows into the ventricles, pressure in the atria falls and although initially the ventricular pressure continues to fall until complete relaxation, pressure then rises again. 

The filling of the ventricles occurs in 3 phases:

• rapid ventricular filling
• diastasis - slower filling
• atrial systole

The P wave can be seen at the end of diastasis, signalling atrial depolarisation.

As the ventricles fill up with blood, the atrioventricular valves start to float up towards the closed position. 

Approximately 100mL of blood is transferred which leads to the changes in atria and ventricular pressure. At the end of this process, each ventricle contains an end-diastolic volume (EDV) of approximately 120-130mL of blood. 

Heart Sounds:

Although ventricular filling is silent, S3 can be heard due to contraction of the Chordae Tendineae and AV ring. It is also associated with Ventricular Dilation.

During atrial contraction, the heart sound S4 can be heard due to the vibrations of the ventricular wall.

Did you know..?

Atrial systole contributes approximately 30% of the EDV.

In a resting heart, the ventricles are approximately 90% full before atrial contraction occurs