What does the diastolic blood pressure measure?

• A. Pressure during heart contraction
• B. Pressure in the arteries when the heart relaxes
• C. Average arterial pressure
• D. Venous pressure only

Answer: (B)

Diastolic blood pressure is the pressure in the arteries when the heart is relaxed between beats. This relaxation phase, called diastole, is when the ventricles fill with blood, and the arteries momentarily experience their lowest pressure in the cardiac cycle. On a reading like 120/80, the diastolic value is the bottom number (80), representing that minimum arterial pressure.

This is different from the pressure during heart contraction, which is the systolic pressure—the top number. It’s also not an “average” arterial pressure (that would be mean arterial pressure), nor is it venous pressure, which refers to the pressure in the veins.