Hypertension or high blood pressure is a medical disorder that is characterized by the presence of persistently elevated blood pressure in the arteries. Blood pressure is the measurement of the force of the blood pumped by the heart on the walls of the arteries. The normal level of blood pressure is represented as the reading of 120/80 mmHg, where 120 is the systolic pressure (highest pressure in the arteries) and 80 is the diastolic pressure (lowest pressure in the arteries). A blood pressure reading between 120/80 and 139/89 is referred to as prehypertension. A blood pressure reading of 140/90 mmHg or above is referred to as hypertension. There are two types of hypertension: essential (without any cause) and secondary (has a direct cause such as kidney disease and birth control pills). High blood pressure can be present for many years without causing any symptoms. Uncontrolled hypertension increases the risk of developing serious medical disorders such as heart attack and stroke.