During which phase of the cardiac cycle does the aortic valve open?

Explanation

## Timing of Aortic Valve Opening ### Aortic Valve Opening Mechanism The aortic valve opens when left ventricular pressure exceeds aortic pressure. This occurs during the **rapid ventricular ejection phase** (also called the rapid ejection phase), which is the first and fastest phase of systole. ### Cardiac Cycle Phases | Phase | Valve Status | Pressure Relationship | Duration | |-------|--------------|----------------------|----------| | Isovolumetric contraction | All valves closed | LV > LA, LV < Ao | ~0.05 s | | Rapid ventricular ejection | **Aortic open**, mitral closed | LV > Ao | ~0.1 s | | Reduced ventricular ejection | Aortic open, mitral closed | LV still > Ao | ~0.1 s | | Isovolumetric relaxation | All valves closed | LV < Ao, LV > LA | ~0.08 s | **Key Point:** The aortic valve opens as soon as LV pressure exceeds aortic diastolic pressure (~80 mmHg), allowing blood to be ejected into the aorta. This marks the transition from isovolumetric contraction to the ejection phase. **High-Yield:** The aortic valve closure occurs when aortic pressure exceeds LV pressure at the end of reduced ejection, producing the dicrotic notch on the aortic pressure curve. **Clinical Pearl:** Aortic stenosis delays aortic valve opening and prolongs isovolumetric contraction time, which can be detected by echocardiography.