Everyone would like to have healthy blood pressure. But what exactly does that mean? When your doctor takes your blood pressure, it’s expressed as a measurement with two numbers, with one number on top (systolic) and one on the bottom (diastolic), like a fraction. For example, 120/80 mm Hg. The top number refers to the amount of pressure in your arteries during the contraction of your heart muscle. This is called systolic pressure. The bottom number refers to your blood pressure when your heart muscle is between beats. This is called diastolic pressure.