Blood pressure in the ventricle rises rapidly due to ventricular contraction. This causes ventricular pressure to rise above atrial pressure. Closing of the valve is caused by the reversal of the pressure gradient between the atrium and the ventricle. The blood pressure in the ventricle continues to rise due to contraction of the ventricular myocardium. No blood is ejected from the ventricle until the pressure in the ventricle rises above the pressure in the aorta.
Ventricular pressure exceeds aortic pressure, forcing the aortic semi-lunar valve open.
The volume of blood in the ventricle drops as blood is ejected into the aorta. This is known as the rapid ejection phase of ventricular emptying. The blood pressure in the ventricle and aorta rise due to the continued contraction of the ventricular myocardium and the rapid increase in the volume of blood in the aorta. This distends the aorta. Ventricular pressure drops below aortic pressure due to the relaxation of the ventricular myocardium.