When ventricular systole begins intraventricular pressure increases rapidly closing the atrioventricular (AV) valves.?

When ventricular systole begins, intraventricular pressure increases rapidly, which causes the atrioventricular (AV) valves to close. This is because the pressure in the ventricles becomes greater than the pressure in the atria, causing the AV valves to snap shut. This prevents blood from flowing back into the atria during systole.