During isovolumetric contraction, which of the following is true about the volume of blood in the heart?

During isovolumetric contraction, the volume of blood in the heart remains constant while the pressure increases. This phase occurs after the ventricles have filled with blood and the valves are closed, preventing any blood from entering or leaving the ventricles. As the myocardial fibers contract, the pressure within the ventricles rises sharply because there is no change in volume—the walls of the ventricles are generating force against a closed system.

The significance of this phase is that it prepares the ventricles for the subsequent ejection of blood into the aorta and pulmonary artery. Since the volume does not change during this contraction, it allows for an effective build-up of pressure, ensuring that the ventricles can push blood into the circulation once the aortic and pulmonary valves open.

Other options do not accurately reflect this physiological understanding. The volume does not increase rapidly nor does it decrease during this phase, nor is there excessive filling that would cause overflow. The isovolumetric contraction phase is characterized by this unique state of constant volume coupled with rising pressure as a key mechanism of cardiac function.