What Is High Blood Pressure?

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A reading of 120 over 80 falls in the normal range.

Blood pressure is expressed in millimeters of mercury, or mm Hg. High blood pressure is defined as a systolic blood pressure reading greater than 140 mm Hg or a diastolic blood pressure reading greater than 90 mm Hg. 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.

	Systolic Pressure	Diastolic Pressure
Normal	Less than 130	Less than 85
High Normal	130 to 139	85 to 89
Stage 1 High Blood Pressure	140 to 159	90 to 99
Stage 2 High Blood Pressure	160 to 179	100 to 109
Stage 3 High Blood Pressure	180 or higher	110 or higher

For more information about high blood pressure, see the next page.

High Blood Pressure Numbers