Final answer:
In an isovolumetric contraction, the heart experiences a change in pressure without a change in chamber volume, as the ventricular muscles contract but the atrioventricular and semilunar valves prevent blood ejection and inflow respectively.
Step-by-step explanation:
In the beating heart, an isovolumetric contraction is a change in pressure without a change in chamber volume. During this phase, the muscles of the ventricle contract, and the pressure of the blood within the chamber increases, but since the semilunar valves have not yet opened, and the atrioventricular valves have closed to prevent backflow, the volume of the chamber remains the same. This part of the cardiac cycle is critical to understand as it reflects the heart's behavior in the phase where it prepares to pump blood but has not yet begun the ejection phase.