Blood pressure is the force that sends blood through the arteries from the heart c. Increased blood pressure puts a strain on your circulatory system. The blood pressure system is divided. It's two numbers, systolic pressure is the top number. and the diastolic pressure is the lower number. Both are recorded as mm Hg (millimeters of mercury), which indicates how high the mercury column is raised by the pressure. The systolic pressure is the highest pressure when the heart contracts. The diastolic pressure is the lowest pressure during contractions. Normal is 120/80. The American Heart Association defines adult hypertension as 140 mm Hg or higher systolic and/or 90mm Hg or diastolic higher.