At the beginning of systole, when ventricular pressure exceeds atrial pressure, the av valves close and the semilunar valves also remain closed because the pressure within the ventricles is still not sufficiently strong to force them open. at this point there is no flow of blood in or out of the ventricles. this phase is known as

isovolumetric contraction

Explanation:

According to studies conducted by various medical professionals, I can say that this phase is known as isovolumetric contraction. This is the phase 2 of the cardiac cycle, in which the ventricles contract and while there is no change in volume and all the heart valves are closed. Just as described in the question.

aed pads should be placed in the middle of the child's chest. this ensures that the electricity can properly run through the child's body and hopefully cause his/her heart to start again. hope this : )