Hypertension is defined as elevated blood pressure in the arteries. It is a major cause of kidney failure in the United States. As a person's heart muscle contracts, it pushes blood into the major arteries. It is the pressure within the arteries that is measured in blood pressure readings. The first value of this measurement is called the systolic pressure, which is usually 100 to 130 mmHg (millimeters of mercury) . The second value, the diastolic pressure, is normally between 70 and 80 mmHg. A normal blood pressure might be expressed as 110/70 (110 over 70).