According to the American Heart Association, nearly one third of adults have hypertension (defined as sustained high blood pressure of 140 /90 mmHg and above). Uncontrolled high blood pressure greatly increases the risk of heart disease and stroke - the first and third leading causes of death in developed nations. Because there are no symptoms, many people with hypertension do not know they have it. The only way to tell is to have an accurate check of your blood pressure.