About 25% of U.S. adults have high blood pressure (hypertension). If untreated, high blood pressure eventually damages the heart, brain, eyes, and kidneys. The higher the blood pressure, the greater the risk that complications, such as heart attack and stroke, will develop. There is usually no obvious cause for hypertension, although it is more common in middle-aged and older people than in young people. Blood pressure can be measured at home or in a doctor's office with a blood pressure cuff. Blood pressure readings give two numbers, systolic (the higher number) and diastolic (the lower number) pressures. Normal blood pressures are lower than 140 mm Hg (systolic) and lower than 90 mm Hg (diastolic).