Both the Systolic and Diastolic blood pressure readings are important but the most important of those two is the Systolic blood pressure reading.
The systolic number is the reading that measures the pressure in the blood vessels during the split-second when the heart is pumping out blood; the diastolic number is the reading that measures the blood pressure when the heart is resting.
The people in the medical industry have once before emphasized the diastolic reading as being the most important number in blood pressure, but an accumulation of recent findings now show that the systolic reading is as -- if not more -- important in diagnosing and treating high blood pressure, or hypertension.
So the more important number to look at when reading blood pressure is the systolic number which is the first number in the blood pressure reading.
If the systolic number goes above 120 then it's getting into prehypertension and anything above 140 it's getting more severe and could lead to a heart attack, stroke or heart disease.