Propranolol, the first beta-adrenergic receptor blocking agent to receive approval from the Food and Drug Administration for marketing, will soon be available for general use in the United States. Because of the mass of information that has accumulated relating to the physiological, metabolic, and clinical effects of this type of pharmacologic agent (1), great interest has developed in the clinical application of beta-adrenergic receptor inhibition. However, the widespread enthusiasm attendant upon the imminent availability of drugs that can specifically block beta receptors should be tempered. Although these agents have been shown to have considerable therapeutic efficacy, there is ample evidence