Systolic and diastolicSystole · Diastole

Systole is the phase in which the heart contracts and ejects blood, producing the higher of the two blood-pressure numbers. Diastole is the relaxation phase in which the chambers refill, producing the lower number. A reading of 118 over 76 means 118 during systole and 76 during diastole.

It matters because the two carry different information. Systolic pressure rises with age as arteries stiffen and is the stronger predictor of cardiovascular events in people over about fifty; diastolic pressure is relatively more informative in younger adults. The gap between them, the pulse pressure, is itself a marker of arterial stiffness.

In practice a single reading means little. Pressure varies through the day, rises with stress and with a rushed arrival at the clinic, so several readings taken calmly across days give a far truer picture.