There is evidence that the beta blocking drugs are useful in angina pectoris, inhibiting the tachycardia of exercise and other forms of stress, such as emotion. In myocardial infarction, there is experimental evidence in animals and man for the effectiveness of these drugs in restoring the supply/demand balance of the ischaemic areas, and thus limiting infarct size. They may act partly by redistributing the coronary blood flow from areas of relatively good perfusion to those less well supplied. Cardiac pain is reduced in angina and also post-infarction. In contrast to the usual haemodynamic effect of beta blockade, muscle contraction of the ischaemic myocardium may be improved. Beta adrenergic blocking drugs may reduce the incidence of reinfarction when given as a prophylactic to post-infarction patients.