Regarding the events of the cardiac cycle, all of the following statements are TRUE EXCEPT:

## Analysis of Cardiac Cycle Events ### Correct Statements (Options 0, 2, 3) **Option 0 — Isovolumetric Contraction:** - Occurs immediately after mitral valve closure (end of atrial systole) - Ventricular volume remains constant; pressure rises sharply - Ends when aortic valve opens (when LV pressure exceeds aortic pressure) - ✓ TRUE **Option 2 — Atrial Contribution to Ventricular Filling:** - Atrial systole ("atrial kick") contributes 20–30% of LV filling in normal rhythm - Becomes critical in tachycardia and atrial fibrillation - ✓ TRUE **Option 3 — Second Heart Sound (S2):** - Produced by closure of aortic and pulmonary valves - Occurs at the END of ventricular systole / START of isovolumetric relaxation - Marks the transition from systole to diastole - ✓ TRUE ### Incorrect Statement (Option 1) — THE ANSWER **Option 1 — Aortic Pressure vs. LV Pressure During Rapid Ejection:** - During rapid ejection, LV pressure is **HIGHER** than aortic pressure - This pressure gradient drives blood out of the ventricle - The statement claims aortic pressure exceeds LV pressure — this is **BACKWARDS** - If aortic pressure exceeded LV pressure, the aortic valve would close and ejection would cease - ✗ FALSE ### Key Pressure Relationships During Systole | Phase | LV Pressure vs. Aortic Pressure | Valve Status | |-------|----------------------------------|---------------| | Isovolumetric contraction | LV < Aortic | Both closed | | Rapid ejection | **LV > Aortic** | Aortic open | | Reduced ejection | LV > Aortic (narrowing) | Aortic open | | Isovolumetric relaxation | LV < Aortic | Both closed | **Key Point:** For blood to flow from the left ventricle into the aorta, the left ventricular pressure MUST exceed aortic diastolic pressure. The pressure gradient (LV > Aorta) is the driving force for ejection. **High-Yield:** A common exam trap is confusing the direction of pressure gradients. Remember: flow always goes from HIGH to LOW pressure. During ejection, LV pressure is highest in the cardiovascular system at that moment. **Clinical Pearl:** In severe aortic stenosis, the aortic valve opening is restricted, so a very high LV pressure is needed to overcome the valve resistance and maintain ejection. This is why LV hypertrophy develops — the ventricle must generate supranormal pressures to eject blood against the stenotic valve.