Blood pressure is the force the blood exerts against the arterial wall. Blood pressure consists of two values measured in millimeters of mercury (mm Hg): the pressure when the heart beats (systolic pressure), and the pressure when the heart is at rest (diastolic pressure). In adults, values greater than140 mm Hg systolic pressure or values greater than 90 mm Hg diastolic pressure are considered high blood pressure. High blood pressure directly increases the risk of heart attack and stroke.