Blood pressure is the force created by the heart as it pushes blood into the arteries and the circulatory system. When the heart pumps, it causes blood to flow through the arteries and into the arterioles. As the blood goes through the arterioles, the arterioles either contract or expand altering both the amount of blood flow and the resistance to blood flow. If the arterioles remain in a contracted form, they create high blood pressure. The heart must then pump harder because the arterioles are exerting a greater resistance to blood flow. High blood pressure is often called the "silent killer". High blood pressure is called this because there are usually no symptoms. Very high blood pressure can also cause arteries to bulge (aneurysm) or burst (hemorrhage).