In order to evaluate cardiac rate and rhythm in 20 patients with coronary atherosclerotic disease who were engaged in a medically supervised exercise program, continuous ambulatory electrocardiographic monitoring was performed during an exercise training class and the subsequent 24 hours, which included activities at work and home. Sixty-five percent (13) of the 20 patients had abnormal findings on recordings. Of the 20 patients studied, 40 percent (eight) had arrhythmias detected by ambulatory recording that had not been detected either by resting or exercise electrocardiograms. Three patients with ventricular ectopis (multiform premature ventricular beats, couplets, and begeminy) had exercise activities temporarily curtailed and therapy with antiarrhythmic drugs begun, with subsequent resolution or improvement. Two other patients (with recorded heart rates of 160 beats per minute) were instructed to carefully monitor their heart rate in order to not exceed the target maximum. We conclude that 24-hour continuous electrocardiographic monitoring is beneficial in evaluating patients in cardiac exercise programs and frequently influences the management of such patients.