What Is Blood Pressure?

Info: U.S. Department National Heart Lung and Blood Institute

Blood pressure is the force of blood against the walls of arteries. Blood pressure is recorded as two numbers—the systolic pressure (as the heart beats) over the diastolic pressure (as the heart relaxes between beats). The measurement is written one above or before the other, with the systolic number on top and the diastolic number on the bottom. For example, a blood pressure measurement of 120/80 mmHg (millimeters of mercury) is expressed verbally as "120 over 80."

Normal blood pressure is less than 120 mmHg systolic and less than 80 mmHg diastolic.

High Blood Pressure

High blood pressure increases your chance (or risk) for getting heart disease and/or kidney disease, and for having a stroke. It is especially dangerous because it often has no warning signs or symptoms. Regardless of race, age, or gender, anyone can develop high blood pressure. It is estimated that one in every four American adults has high blood pressure. Once high blood pressure develops, it usually lasts a lifetime. You can prevent and control high blood pressure by taking action.

What Are High Blood Pressure and Prehypertension?

Blood pressure is the force of blood against the walls of arteries. Blood pressure rises and falls during the day. When blood pressure stays elevated over time, it is called high blood pressure.

The medical term for high blood pressure is hypertension. High blood pressure is dangerous because it makes the heart work too hard and contributes to atherosclerosis (hardening of the arteries). It increases the risk of heart disease and stroke, which are the first- and third-leading causes of death among Americans. High blood pressure also can result in other conditions, such as congestive heart failure, kidney disease, and blindness.

A blood pressure level of 140/90 mmHg or higher is considered high. About two-thirds of people over age 65 have high blood pressure. If your blood pressure is between 120/80 mmHg and 139/89 mmHg, then you have prehypertension. This means that you don't have high blood pressure now but are likely to develop it in the future. You can take steps to prevent high blood pressure by adopting a healthy lifestyle.

Those who do not have high blood pressure at age 55 face a 90 percent chance of developing it during their lifetimes. So high blood pressure is a condition that most people have at some point in their lives.

Both numbers in a blood pressure test are important, but for people who are 50 or older, systolic pressure gives the most accurate diagnosis of high blood pressure. Systolic pressure is the top number in a blood pressure reading. It is high if it is 140 mmHg or above.

What is systolic blood pressure?

Systolic pressure is the force of blood in the arteries as the heart beats. It is shown as the top number in a blood pressure reading. High blood pressure is 140 and higher for systolic pressure. Diastolic pressure does not need to be high for you to have high blood pressure.

If left uncontrolled, high systolic pressure can lead to stroke, heart attack, congestive heart failure, kidney damage, blindness, or other conditions. While it cannot be cured once it has developed, it can be controlled.

Clinical studies have proven that treating a high systolic pressure saves lives, greatly reduces illness, and improves the quality of life. Yet, most Americans do not have their high systolic pressure under control.

What is diastolic blood pressure?

Diastolic pressure is the force of blood in the arteries as the heart relaxes between beats. It's shown as the bottom number in a blood pressure reading.

The diastolic blood pressure has been and remains, especially for younger people, an important hypertension number. The higher the diastolic blood pressure the greater the risk for heart attacks, strokes and kidney failure. As people become older, the diastolic pressure will begin to decrease and the systolic blood pressure begins to rise and becomes more important. A rise in systolic blood pressure will also increase the chance for heart attacks, strokes, and kidney failure. Your physician will use both the systolic and the diastolic blood pressure to determine your blood pressure category and appropriate prevention and treatment activities.

Why Is High Blood Pressure Important?

High blood pressure is dangerous because it makes the heart work too hard. It also makes the walls of the arteries hard. High blood pressure increases the risk for heart disease and stroke , the first- and third-leading causes of death for Americans. High blood pressure can also cause other problems, such as heart failure, kidney disease, and blindness

Effect of High Blood Pressure on Your Body:


High blood pressure is the most important risk factor for stroke. Very high pressure can cause a break in a weakened blood vessel, which then bleeds in the brain. This can cause a stroke. If a blood clot blocks one of the narrowed arteries, it can also cause a stroke.

Impaired Vision

High blood pressure can eventually cause blood vessels in the eye to burst or bleed. Vision may become blurred or otherwise impaired and can result in blindness.


As people get older, arteries throughout the body "harden," especially those in the heart, brain, and kidneys. High blood pressure is associated with these "stiffer" arteries. This, in turn, causes the heart and kidneys to work harder.

Kidney Damage

The kidneys act as filters to rid the body of wastes. Over time, high blood pressure can narrow and thicken the blood vessels of the kidneys. The kidneys filter less fluid, and waste builds up in the blood. The kidneys may fail altogether. When this happens, medical treatment (dialysis) or a kidney transplant may be needed.

Heart Attack

High blood pressure is a major risk factor for heart attack. The arteries bring oxygen-carrying blood to the heart muscle. If the heart cannot get enough oxygen, chest pain, also known as "angina," can occur. If the flow of blood is blocked, a heart attack results.

Congestive Heart Failure

High blood pressure is the number one risk factor for congestive heart failure (CHF). CHF is a serious condition in which the heart is unable to pump enough blood to supply the body's needs

What Causes High Blood Pressure?

The causes of high blood pressure vary. Causes may include narrowing of the arteries, a greater than normal volume of blood, or the heart beating faster or more forcefully than it should. Any of these conditions will cause increased pressure against the artery walls. High blood pressure might also be caused by another medical problem. Most of the time, the cause is not known. Although high blood pressure usually cannot be cured, in most cases it can be prevented and controlled.

Who Can Develop High Blood Pressure?

High blood pressure is common. About 65 million American adults — nearly 1 in 3 — have high blood pressure. It is very common in African Americans, who may get it earlier in life and more often than whites. Many Americans tend to develop high blood pressure as they get older, but this is not a part of healthy aging. Middle-aged Americans face a 90% chance of developing high blood pressure during their lives. Others at risk for developing high blood pressure are the overweight, those with a family history of high blood pressure, and those with prehypertension (120–139/80–89 mmHg).

African Americans

High blood pressure occurs more often among African Americans than whites. It begins at an earlier age and is usually more severe. Further, African Americans have a higher death rate from stroke and kidney disease than whites. The good news is treatment can control high blood pressure. In addition, lifestyle changes can prevent and control high blood pressure. These include losing weight if overweight (losing 10 lbs can help), increasing physical activity (walking 30 minutes per day can help), following a healthy eating plan, that emphasizes fruits, vegetables, and low fat dairy foods, choosing and preparing foods with less salt and sodium, and if you drink alcoholic beverages, drinking in moderation. If lifestyle changes alone are not effective in keeping your blood pressure controlled, there are many blood pressure medications to help you.

How Is Blood Pressure Tested?

Having your blood pressure tested is quick and easy. Blood pressure is measured in millimeters of mercury (mmHg) and recorded as two numbers systolic pressure "over" diastolic pressure. For example, the doctor or nurse might say "130 over 80" as a blood pressure reading.

Both numbers in a blood pressure reading are important. As we grow older, systolic blood pressure is especially important.

To test your blood pressure, your doctor will use a familiar device with a long name. It is called a sphygmomanometer (pronounced sfig'-mo-ma-nom-e-ter), and may look something like this:

Picture of sphygmomanometer and stethoscope

Some blood pressure testing devices use electronic instruments or digital readouts. In these cases, the blood pressure reading appears on a small screen or is signaled in beeps, and no stethoscope is used.

Categories for Blood Pressure Levels in Adults

(Ages 18 Years and Older)

Blood Pressure Level (mmHg)






< 120


< 80





High Blood Pressure  

Stage 1 Hypertension




Stage 2 Hypertension

greater than or equal to160


greater than or equal to100


< means LESS THAN
greater than or equal tomeans GREATER THAN OR EQUAL TO

When systolic and diastolic blood pressures fall into different categories, the higher category should be used to classify blood pressure level. For example, 160/80 mmHg would be stage 2 hypertension (high blood pressure).

Obtain more information from:

National Heart, Lung and Blood Institute  National Heart, Lung and Blood Institute

National Institutes of Health  National Institutes of Health

Department of Health and Human Services  Department of Health and Human Services