The diastolic blood pressure number or the bottom number indicates the pressure in the arteries when the heart rests between beats. This is the time when the heart fills with blood and receives oxygen. A normal diastolic blood pressure number is less than 80. A diastolic blood pressure between 80 and 89 indicates prehypertension. A diastolic blood pressure number of 90 or higher is considered to be hypertension or high blood pressure.