Hypertension is known as the "silent killer" because it does not produce any symptoms, at least none that most people are aware of, until considerable damage has already been done. Untreated high blood pressure is the leading cause for strokes; the added pressure also damages the artery walls increasing fatty plaque being deposited, leading to scarring and hardening of the vessels creating atherosclerosis. As a result it reduce the flow of oxygen to the kidneys, heart, and eyes, or allows a blood clot to form in a narrowed artery.