Overview: May 17th is the World Hypertension Day. High blood pressure occurs when pressure in the blood vessels is high (140/90 mm Hg or more). It is a common condition that can be dangerous if left untreated. Often those affected do not feel any symptoms, so it is called the silent killer. Blood pressure testing is the only way to know about the condition. The day promotes increased awareness of high blood pressure, accuracy in measuring it, and control of non-communicable diseases associated with high blood pressure.