Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

High Blood Pressure (Hypertension)

What Is It?

Blood pressure has two components:

• Systolic pressure is the top number. It represents the pressure the heart generates when it beats to pump blood to the rest of the body.

• Diastolic pressure is the bottom number. It refers to the pressure in the blood vessels between heartbeats.

Blood pressure is measured in millimeters of mercury (mmHg). So blood pressure would be expressed, for example, as 120/80 mmHg.

High blood pressure is diagnosed when one or both of these numbers is too high. High blood pressure is also called hypertension.

Blood pressure is categorized as follows:

Normal: Less than 120/80 mmHg

Prehypertension: 120/80 to 139/89 mmHg

Stage 1 hypertension: 140/90 to 159/99 mmHg

Stage 2 hypertension: 160/100 mmHg and above

Usually, systolic pressure increases as we age. However, after age 60, diastolic pressure usually begins to decline.

Prehypertension is not a disease—yet. But it does mean you are at increased risk for developing high blood pressure.

Why worry about high blood pressure? High blood pressure can damage many organs, including the:

• Brain

• Eyes

• Heart

• Kidneys

• Arteries throughout the body

Hypertension increases your risk of heart attack, stroke, and kidney failure.