High blood pressure (hypertension)

High blood pressure (hypertension) is often called a silent killer because you can have it for years without knowing it. In fact, about 50 million Americans have high blood pressure, but about 30 percent of them don't know it.
Blood pressure is determined by the amount of blood your heart pumps and the amount of resistance to blood flow in your arteries. Your blood pressure normally varies during the day. It can even vary slightly with each beat of your heart. It increases during activity and decreases with rest.
Many people may not view high blood pressure as life-threatening. But uncontrolled high blood pressure can increase your risk of serious health problems. Fortunately, high blood pressure can be detected with a simple test — and once you know you have high blood pressure, you can work with your doctor to control it.