Pronunciation: (BAY-tuh-BLAH-ker)

A type of drug that blocks the action of substances, such as adrenaline, on nerve cells and causes blood vessels to relax and dilate (widen). This allows blood to flow more easily and lowers blood pressure and the heart rate. Beta-blockers are used to treat high blood pressure, chest pain (angina), abnormal heart rate (arrhythmia), congestive heart failure, and several other conditions. They may also shrink certain types of vascular tumors, such as hemangiomas. Also called beta-adrenergic antagonist and beta-adrenergic blocking agent.

Source: NCI Dictionary of Cancer Terms