Blood pressure is the force your blood makes against the walls of your arteries. The pressure is highest when your heart pumps blood into your arteries – when it beats. It is lowest between heart beats, when your heart relaxes. A doctor or nurse will write down your blood pressure as the higher number over the lower number. For instance, you could have a blood pressure of 110/70 (read as “110 over 70″). A blood pressure reading below 120/80 is usually considered normal. Very low blood pressure (lower than 90/60) can sometimes be a cause of concern and should be checked out by a doctor.
   High blood pressure, or hypertension, is a blood pressure reading of 140/90 or higher. Years of high blood pressure can damage artery walls, causing them to become stiff and narrow. This includes the arteries carrying blood to the heart. As a result, your heart cannot get the blood it needs to work well. This can cause a heart attack.
  A blood pressure reading of 120/80 to 139/89 is considered prehypertension. This means that you don’t have high blood pressure now but are likely to develop it in the future.
