Cardiac cycle

SYSTOLE: contraction

The atria contracts pushing the remaining blood into the ventricles

SYSTOLE: Contraction

• There is a short delay to allow the ventricles to fill
• The pressure increases in the ventricles causing the atrioventricular valves to shut
• And so, this causes the semi-lunar valves to open

DIASTOLE: Relaxation

• Blood returns to the atria by the vena cava and pulmonary vein
• The atria fills up, and increases the pressure
• This causes the atrioventricular valve to open
• Blood then moves into the ventricles
• The ventricle walls are relaxed which results in a lowered pressure in the ventricles, a lower pressure in the aorta and pulmonary artery resulting in the semi-lunar valve to shut