AV valve closes as pressure in ventricle exceeds pressure in atrium. Closure of AV valves marks the beginning of isovolumetric contraction phase. Closure of AV valves causes the first heart sound. Closure of AV valves marks the end of ventricular diastole, beginning of systole. 7. pressure in atrium dissipates as walls adjust to the pressure change.
Volume remains constant as pressure rises.
Ejection begins when pressure in the ventricle exceeds the pressure in the aorta, causing the aortic valve to open. Initially, aortic flow rates increase and ventricular volume decreases rapidly. Ventricular pressure falls rapidly. Ventricular volume is constant. This pressure dissipates as the mitral valve opens and ventriclar filling begins.