Arteries are like hoses that carry blood from your heart to the rest of your body. If you put a crimp in a hose, pressure builds up inside it. High blood pressure (also called hypertension) occurs when your blood moves through your arteries at a higher pressure than normal.
What do the numbers mean?
Blood pressure is really two measurements, separated by a slash when written, such as 120/80. You may also hear someone say a blood pressure is "120 over 80."
The first number is the systolic blood pressure. This is the peak blood pressure when your heart is squeezing blood out. The second number is the diastolic blood pressure. It's the pressure when your heart is filling with blood--relaxing between beats.
A normal blood pressure is less than 120/80. High blood pressure is 140/90 or higher. If your blood pressure is between 120/80 and 140/90, you have what is called "prehypertension," which means that if you don’t take important steps, your blood pressure can turn into high blood pressure.