As your heart pumps blood through your arteries, the moving blood exerts pressure against the arterial walls. This force is measured as blood pressure. Your blood pressure rises normally in response to many everyday in?uences, such as exercise, caffeine, medications, or stressful situations, and then returns to a normal level. But if the pressure in your arteries is consistently higher than is healthy, your heart needs to work harder and your blood vessels and heart can become damaged.
Blood pressure is determined by the force of the heart as it contracts (systole) and the resistance of the main arteries and smaller arteries (called arterioles) to blood ?ow. The other force is diastole or relax- ation. Healthy arterioles are muscular and highly elastic and stretch eas- ily as blood is pumped into them. Their ready squeezing action keeps blood moving. When the heart is pumping more blood, as during exer- cise, many of the arterioles expand to accommodate greater blood ?ow. Healthy arteries are also wide open, clear of any buildup or obstruction so that blood can ?ow freely. Diseased arteries lose their elasticity, and pressure rises.