β adrenergic receptor antagonists (also called beta-blockers or β-blockers) were initially developed in the 1960s, for the treatment of angina pectoris but are now also used for  hypertension, congestive heart failure and certain arrhythmias.   In the 1950s, dichloroisoproterenol (DCI) was discovered to be a β-antagonist that blocked the effects of sympathomimetic amines on bronchodilation, uterine relaxation and heart stimulation. Although DCI had no clinical utility, a change in the compound did provide a clinical candidate, pronethalol, which was introduced in 1962.