Beta-adrenergic blocking agents are widely employed in the primary and secondary prevention of cardiovascular disease.In the first phase of this study, it was determined that there are large changes in the degree of cardiac electrical system stimulation during the course of the day. It was shown that the heart's electrical sys. was most stimulated in the early A.M. The obj. of this study is to determine the effects of beta blocker drugs on the heart's elect. sys. during the course of one complete twenty-four period.