When heart beats, it contracts and pushes blood through the arteries to the rest of the body. This force creates pressure on the arteries. This is called systolic pressure. The diastolic pressure on the other hand, indicates the pressure in the arteries when the heart rests or relaxes between beats. A normal systolic blood pressure is 120 mm of Hg. A normal diastolic blood pressure number is 80 mm of Hg.