During which phase of the cardiac cycle is the velocity of blood flow across the aortic valve the HIGHEST?
- A Isovolumetric contraction
- B Reduced ejection phase (last two-thirds of systole)
- C Rapid ejection phase (early systole, first third of ejection) ✓
- D Isovolumetric relaxation
Correct answer: C. Rapid ejection phase (early systole, first third of ejection)
Explanation
After aortic valve opening, rapid ejection (early systolic ejection, first ~30% of ejection time) accounts for approximately 70% of stroke volume and produces peak aortic flow velocity (~100 cm/s). The aortic valve closes during the reduced ejection phase, when flow is decelerating. Isovolumetric contraction and relaxation are closed-valve periods with no aortic flow. This physiological peak flow velocity is the basis for peak flow measurements by echocardiographic Doppler to estimate aortic valve gradients.
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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