Blood pressure is simply the pressure inside your blood vessels, both as your heart is pumping blood through the vessels and while the heart is relaxed. High and low blood pressure can cause health problems, so keeping your blood pressure at a proper level is essential to good long-term health. Many people consider a blood pressure of 120/80 to be normal. A few of the things that can make a person's blood pressure change include nicotine use, posture, and the person's amount of tension and level of exercise. Blood pressure can also run high or low in families. Maintaining a normal blood pressure is an important part of lowering your risk of organ damage or a heart attack or stroke.