Prehypertension is when blood pressure (the pressure of the blood against the walls of the arteries) is consistently ranging 120-139/80-89. People with pre-hypertension are likely to develop high blood pressure unless steps are taken to control it. Blood pressure is optimal at less than 120/80 and is considered high if it is above 140/90. High blood pressure increases the risk for heart attack, angina, stroke, kidney failure and peripheral artery disease.