What happens to the ventricles during isovolumetric contraction?

During isovolumetric contraction, the ventricles are in a phase of the cardiac cycle where the muscular walls contract, leading to an increase in pressure within the ventricles. This contraction occurs after the ventricles have filled with blood during diastole and just before the semilunar valves open to allow blood to be ejected into the arteries. However, during this specific phase, even though the pressure is rising as the ventricles contract, there is no change in the volume of blood within them because all the valves (AV and semilunar) are closed.

This is a critical moment because it allows the pressure to build sufficiently to exceed the pressure in the aorta and pulmonary artery before the semilunar valves open. The inability of blood to flow in or out while the ventricles are contracting is what characterizes this phase as "isovolumetric," meaning the volume of the ventricles remains constant. Therefore, the understanding of pressure dynamics, valve status, and the overall progression of the cardiac cycle confirms that option B is accurate.