How the Heart Works
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Blood Pressure
Blood vessels maintain pressure at all times to allow the blood to flow throughout the body. When the ventricles contract, pressure rises, and blood is pumped out into the arteries. Between heartbeats, while the ventricle is refilling, the pressure falls.
The two numbers used to measure blood pressure are referred to as the systolic and diastolic pressures. The systolic blood pressure is the highest pressure achieved when the heart is contracting and forcing blood into the arteries. The diastolic blood pressure is the lowest pressure that occurs when the heart is relaxed or when the left ventricle is refilling. A typical blood pressure reading is written as a fraction with the systolic number over the diastolic rate (e.g., 120/80).