Blood pressure is the force of blood pushing against the walls of your arteries as your heart pumps it through your body. Think of it like water pressure in a garden hose: when you turn on the faucet, the water pushes outward against the inside of the hose. Your blood does the same thing in your blood vessels.

Doctors measure blood pressure with two numbers. The first (higher) number is systolic pressure, which measures the force when your heart squeezes and pushes blood out. The second (lower) number is diastolic pressure, which measures the pressure between heartbeats when your heart relaxes. A doctor might say someone has a blood pressure of “120 over 80,” written as 120/80.

Blood pressure that's too high means the heart is working harder than it should, like a pump straining against too much resistance. Blood pressure that's too low means not enough blood is reaching all parts of the body. Healthy blood pressure keeps your organs, muscles, and brain supplied with the oxygen and nutrients they need to function properly.

When someone gets nervous or exercises hard, their blood pressure rises temporarily. That's normal. Doctors check blood pressure to make sure it stays in a healthy range over time because consistently high blood pressure can damage the heart and blood vessels.