What prevents the blood from leaving the ventricles during isovolumetric contraction?

during the isometric contraction, the pressure in ventricle is less than the pressure in the aorta. there is no blood can leave the ventricle yet because the ventricle is trying to increase its pressure . if the pressure exceeds80mmhg in the ventricle , then the ventricle in the blood must leave through aortic values. so the pressure is what prevents blood from leaving the ventricle.