Beta blockers are a type of medicine that is used to lower blood pressure, treat chest pain (angina) and heart failure, and to help prevent a heart attack. Beta blockers relieve the stress on your heart by slowing the heart rate and reducing the force with which your heart muscles contract to pump blood. They also help keep blood vessels from constricting in your heart, brain, and body. If you have a heart attack, you should get a prescription for a beta blocker before you leave the hospital.