During the isovolumetric relaxation phase of the cardiac cycle, which of the following pressure relationships is correct?

• A Left ventricular pressure > Aortic pressure with both falling
• B Aortic pressure > Left ventricular pressure > Left atrial pressure ✓
• C Left atrial pressure > Left ventricular pressure > Aortic pressure
• D Left ventricular pressure falls below left atrial pressure, opening the mitral valve

Explanation

During isovolumetric relaxation, the aortic valve has just closed (because LV pressure fell below aortic pressure) but the mitral valve has not yet opened (because LV pressure has not yet fallen below left atrial pressure). Thus aortic pressure > LV pressure > left atrial pressure. This phase ends when LV pressure drops below left atrial pressure, causing the mitral valve to open and initiating rapid ventricular filling.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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