Beta-blocker, drug that affects the transmission of signals at beta-receptors, parts of the sympathetic nervous system located in the heart, lungs, kidneys, and blood vessels. Beta-blockers (or beta-adrenergic blocking agents) interfere with the stimulation of the beta-receptors. They thereby lower blood pressure and heart rate. They are used in the treatment of hypertension and cardiac arrrhythmia.
See also: Drug.