What is the term for the phase of the cardiac cycle where contraction occurs without a change in volume?

The term that describes the phase of the cardiac cycle where contraction occurs without a change in volume is known as isovolumetric contraction. During this phase, the ventricles contract, which increases the pressure inside them, but all heart valves are closed. This means that even though the muscle fibers are shortening and generating force, the volume of blood within the ventricles remains constant. Isovolumetric contraction occurs between the end of diastole and the beginning of systolic ejection, typically when the mitral and aortic valves are closed.

Understanding this phase is critical for comprehending how the heart operates during the cardiac cycle. It highlights the heart's ability to generate pressure to overcome the aortic and pulmonary artery pressures necessary for blood ejection in the subsequent phase of the cycle. This concept is essential in critical care, as it reflects the heart's contractility and the dynamics of stroke volume and cardiac output.