Beta blockers (sometimes written as β-blocker) are a class of drugs used for various indications, but particularly for the management of cardiac arrhythmias, cardioprotection after myocardial infarction (heart attack), and hypertension. Propranolol was the first clinically useful beta adrenergic receptor antagonist. Invented by Sir James W. Black, it revolutionized the medical management of angina pectoris and is considered to be one of the most important contributions to clinical medicine and pharmacology of the 20th century. Beta blockers may also be referred to as beta-adrenergic blocking agents, beta-adrenergic antagonists, or beta antagonists.