Effect of beta-adrenergic blocking agents on the circadian occurrence of ischemic cardiovascular events. Clinical observations suggest that beta-adrenergic blocking agents can modify the circadian occurrence of a variety of ischemic events. Morning awakening is associated with a rapid increase in blood pressure and pulse, serum catecholamine content and platelet activation, at a time of decreased blood thrombolytic activity. Beta-adrenergic blocking agents have the potential to modify many of these events. Current data indicate that these agents modify blood pressure and pulse, but do not prevent their early morning increase. In addition, beta-adrenergic blocking agents decrease ventricular ectopy and its circadian variation. Recent studies in humans indicate, however, that metoprolol does not affect the circadian increase in platelet activity or serum catecholamines. The specific mechanism by which beta blockers affect the circadian occurrence of ischemic events remains uncertain. 