Name the four phases of the cardiac cycle and the valve events associated with each phase.

• A. Isovolumetric contraction (AV valves closed, semilunar valves closed), ventricular systole with ejection (semilunar valves open, AV valves closed), isovolumetric relaxation (all valves closed), ventricular filling (AV valves open, semilunar valves closed)
• B. Rapid filling, atrial contraction, isovolumetric contraction, ventricular ejection
• C. Atrial contraction, ventricular ejection, isovolumetric relaxation, ventricular filling
• D. Diastole, systole, isovolumetric contraction, diastasis

Answer: (A)

The four phases tested are isovolumetric contraction, ventricular ejection, isovolumetric relaxation, and ventricular filling. The valve events that define each phase are: during isovolumetric contraction, both AV valves (mitral and tricuspid) and semilunar valves (aortic and pulmonary) are closed, so the ventricle contracts with no change in volume. Then, ventricular ejection begins when the semilunar valves open and the AV valves remain closed, allowing blood to be ejected into the aorta and pulmonary artery. Next is isovolumetric relaxation, where all valves are closed again as the ventricle relaxes and pressure falls but volume stays the same. Finally, ventricular filling occurs when the AV valves open and the semilunar valves stay closed, allowing blood to flow from the atria into the ventricles; this phase includes rapid filling, diastasis, and atrial contraction completing the fill. Other sequences mix up the timing or group broad periods (like diastole or systole) rather than describing the valve-opening/closing pattern that defines these four phases.