When your heart beats, it pumps blood round your body to give it the energy and oxygen it needs. As the blood moves, it pushes against the sides of the blood vessels.
The strength of this pushing is your blood pressure. If your blood pressure is too high, it puts extra strain on your arteries (and your heart) and this may lead to heart attacks and strokes.
Having high blood pressure (hypertension) is not usually something that you feel or notice. It does not tend to produce obvious signs or symptoms. The only way to know what your blood pressure is, is to have it measured.
Blood pressure is measured in ‘millimetres of mercury’ (mmHg) and is written as two numbers. For example, if your reading is 120/80mmHg, your blood pressure is ‘120 over 80’.
Every blood pressure reading consists of two numbers or levels. They are shown as one number on top of the other.
The first (or top) number is your systolic blood pressure. It is the highest level your blood pressure reaches when your heart beats.
The second (or bottom) number is your diastolic blood pressure. It is the lowest level your blood pressure reaches as your heart relaxes between beats.