Elevated blood pressure without a known cause. It occurs when the systolic pressure is consistently over 140 mm Hg, or the diastolic blood pressure is consistently over 90 mm Hg. Blood pressure is determined by the amount of blood pumped, by the actions of the heart, and by the size and condition of the arteries. Untreated high blood pressure can cause narrowing of the arteries (atherosclerosis) and result in heart attacks, strokes, and kidney disease.