The systolic blood pressure is the top number of a blood pressure reading . This shows the maximum pressure in the blood vessels. Pressure is highest as the heart contracts and circulates blood throughout the body. The diastolic blood pressure is the bottom number of a blood pressure reading. It shows the lowest pressure in the blood vessels.
Pressure is lowest between heartbeats, when the heart is at rest.
The National Institutes of Health has further defined high blood pressure. These categories are for people 18 years and older who do not take medication for high blood pressure and do not have a short-term serious illness. These categories are as follows. Normal blood pressure is a systolic blood pressure of less than 130, and a diastolic pressure of less than 85. High normal blood pressure is a systolic blood pressure of 130 to 139, and a diastolic pressure of 85 to 89.