During the cardiac cycle, the aortic valve closes at the end of which phase?

Explanation

## Timing of Aortic Valve Closure **Key Point:** The aortic valve closes when ventricular pressure falls below aortic pressure, which occurs immediately after the end of ventricular ejection. ### Phases of the Cardiac Cycle | Phase | Duration | Valve Status | Pressure Relationship | |-------|----------|--------------|----------------------| | Ventricular filling | Early diastole | AV open, aortic closed | LV < LA | | Isovolumetric contraction | Early systole | Both closed | LV pressure rising | | Ventricular ejection | Mid-to-late systole | AV closed, aortic open | LV > Aortic | | Isovolumetric relaxation | Early diastole | Both closed | LV pressure falling | **High-Yield:** Aortic valve closure occurs at the **dicrotic notch** on the aortic pressure curve, marking the end of systole. The closure is passive — determined entirely by the pressure gradient reversal when ventricular pressure drops below aortic pressure. **Clinical Pearl:** The second heart sound (S2) is produced by the closure of both the aortic and pulmonary valves at the end of ventricular ejection. Aortic valve closure slightly precedes pulmonary valve closure on the left side of the chest due to higher LV pressure. **Mnemonic:** **AEIOU** — Aortic valve closes at End of Isovolumetric relaxation? **No** — it closes at the End of ventricular **Ejection** (when LV pressure < aortic pressure).