Blood pressure is measure in millimeters of mercury (mmHg) and recorded as two numbers, systolic and diastolic. Systolic is the top number (also the higher one), which measure the pressure in the arteries when the heart beats, so when its muscles contract. Diastolic the bottom number (also the lower one), which measures the pressure in the arteries between heart beats, so when the muscles relax and refill with blood. 
×