diastolic pressure

Diastolic pressure is the ‘bottom number’ in a blood pressure reading—the lowest pressure remaining in the arteries while the heart relaxes and refills between beats. It is the steady ‘background’ pressure the arteries never drop below.

It reflects the pressure during ventricular diastole, sustained by the elastic recoil of the large arteries squeezing on the blood they hold while the heart is not ejecting. Diastolic pressure depends heavily on systemic vascular resistance—the tone of the small arteries and arterioles—and on heart rate, since a faster rate shortens the time available for the pressure to fall.

Diastolic pressure tends to matter more in younger and middle-aged adults, and notably it also determines how well the heart muscle itself is fed: the coronary arteries supplying the left ventricle fill mainly during diastole, so an excessively low diastolic pressure can compromise the heart’s own blood supply. Both very high and very low diastolic values can be meaningful, so it is read in context with the systolic number, not alone.