Blood pressure measures the force of blood pushing outwards on your arterial walls. It's written as two numbers, such as 112/78 mm Hg. High Blood Pressure means the pressure in your arteries is elevated. The top, systolic, number is the pressure when the heart beats. The bottom, diastolic, number is the pressure when the heart rests between beats. Optimal blood pressure is less than 120 mm Hg systolic and 80 mm Hg diastolic. Blood pressures of 120-139 mm Hg systolic and/or 80-89 mm Hg diastolic are considered prehypertension. Blood pressure is considered high if it is 140 mm Hg systolic and/or 90 mm Hg diastolic or higher. High blood pressure increases the risk for heart attack, angina, stroke, kidney failure and peripheral artery disease (PAD) and death.