Hypertension (or high blood pressure) is a condition where the pressure of the blood flowing through the arteries of the body is higher than it should be. Much like the pressure of the air in a tire, if the pressure of the blood is too high it can damage the arteries and organs of the body. Just like the tire, if the pressure suddenly becomes very high, catastrophic events can happen. Similarly, if the pressure remains somewhat elevated for a long enough period of time, premature wear and failure can occur.
Hypertension has its worst effects on the heart, kidneys, eyes, and brain. High blood pressure is a risk factor for heart attack, stroke, kidney failure, hemorrhages of the retina of the eye, and generalized atherosclerosis (hardening of the arteries all over the body).