This 3D animation from The Human Atlas explains Blood Pressure.

The heart is a beating muscle that pumps oxygen-rich blood to the body through a network of arteries and veins. What we commonly call "blood pressure" is the measurement taken when the heart's left ventricle contracts, and blood is forced through the arteries.

As the blood travels from the heart, it exerts pressure against the walls of the arteries. This is referred to as blood pressure. Blood pressure is used to evaluate the force and amount of blood being pumped from the heart as well as the flexibility and condition of the arteries.

There are two components of a blood pressure measurement. The first is the systolic pressure, which is recorded when blood pressure is at its maximum during contraction of the left ventricle. The second component is diastolic pressure. This measurement is obtained when the blood pressure is at its lowest point when the heart is at rest between beats.

The combined measurement is read as the systolic pressure over the diastolic pressure. Abnormally high pressure within the arteries is called hypertension, or high blood pressure. Hypertension is usually diagnosed when blood pressure measurements are higher than 140 mmHg systolic and 90 mmHg diastolic on three separate occasions.

Hypertension is linked with many medical conditions such as atherosclerosis, congestive heart failure, stroke, heart attack, and kidney damage to name a few. If left untreated, hypertension can seriously damage the heart and blood vessels. The good news is that patients with hypertension can usually control their disease with medication and with changes to diet and lifestyle.