The other component of the blood pressure reading is the diastolic blood pressure, which is the pressure exerted by blood on to the wall of arteries when the heart is relaxed. A typical blood pressure reading is reported as the systolic blood pressure number over the dyastolic blood pressure number (e.g., 120/80).
Under normal conditions, the systolic number is higher than the dyastolic number, which is why the systolic pressure is always the higher of the two numbers in the blood pressure reading.
By definition, the upper level of normal systolic blood pressure is 140 millimeters of mercury (mmHg), while the upper level of normal dyastolic blood pressure is 90mmHg.
Blood pressure that is persistently higher than 140/90 is the number one risk factor for stroke.
