Blood pressure is a measurement of the pressure in your arteries during the active and resting phases of each heartbeat.
Systolic pressure. The top number in a blood pressure reading is the amount of pressure your heart generates when pumping blood through your arteries to the rest of your body.
Diastolic pressure. The bottom number in a blood pressure reading refers to the amount of pressure in your arteries when your heart is at rest between beats.
Throughout the day, blood pressure varies, depending on body position, breathing rhythm, stress level, physical condition, medications you take, what you eat and drink, and time of day. Blood pressure is usually lowest at night and rises sharply on waking.