When the heart pumps blood into the arteries, the blood flows with a force pushing against the walls of the arteries. This force is called the blood pressure. When your blood pressure is measured, it is a measure of how hard the heart has to work to pump the blood. When the arteries become hardened and narrowed with cholesterol plaque (atherosclerosis) and calcium (arteriosclerosis), the heart has to strain much harder to pump blood through them.
This makes the blood pressure go abnormally high. High blood pressure is also called hypertension.
What makes high blood pressure important is that it usually causes no symptoms but can still cause serious complications.
Blood pressure is measured with a blood pressure cuff and recorded as 2 numbers, such as 120/80 mm Hg (millimeters of mercury).
The top, larger number is called the systolic pressure. This is the pressure generated when the heart contracts (pumps). It reflects the pressure of the blood against arterial walls.
The bottom, smaller number is called the diastolic pressure. This reflects the pressure in the arteries while the heart is filling and resting between heartbeats.