About Hypertension According to the American Heart Association, as many as 50 million Americans have hypertension, but about one-third don't know they have it.  Thus, hypertension is often called the "silent killer" because you can have it for years without knowing it.  Elevated blood pressure indicates that the heart is working harder than normal, putting the heart, the arteries and other major organs under a greater strain. Left untreated, hypertension can lead to coronary heart disease, stroke and kidney failure. Blood pressure is the force in the arteries when the heart beats (systolic pressure - SP) and when the heart is at rest (diastolic pressure - DP).  High blood pressure (HBP) or hypertension is defined as systolic blood pressure of 140 mm Hg (millimeters of mercury) or greater OR a diastolic blood pressure of 90 mm Hg or greater.