Beta-blockers prevent natural chemicals, neurotransmitters, from over-stimulating and damaging the body. These neurotransmitters can attach to beta-receptors located all over the body including the heart, kidneys, and eyes. Neurotransmitters that attach to beta-receptors can cause a faster heartbeat, narrower blood vessels, and more fluid pressure in the eyes. Beta-blockers compete with neurotransmitters to attach to the beta-receptors and prevent their stimulation. Beta-blockers can target just one or a few different locations to block the receptors. In the heart, blocking the receptors slows the heart rate. In the kidneys, blocking the receptors affects a hormone, renin, and keeps the blood vessel walls open. In the eye, blocking the receptors decreases fluid pressure.