Transtelephonic monitoring of a single-lead electrocardiogram and on-demand 2-way voice communication were accomplished at 1,865 exercise sessions for 67 cardiac patients. Exercise sessions occurred either at the patients' homes or at remote hospital sites and began an average of 25 or 14 weeks, respectively, after hospital dismissal. Monitoring centers provided experienced nurses to direct all exercise sessions. The transtelephonic monitoring equipment was reliable with only one instance of system failure observed. A broad spectrum of patients with coronary artery disease, including some classified at higher risk, participated in the program. Patients exercised with a variety of equipment (cycle ergometer, treadmill, arm ergometer, cross-country ski simulator, combination arm-leg cycle ergometer, rowing machine), for 30 to 50 minutes, 1 to 3 times each week. No medical emergencies occurred, although 18 specific problems were discovered that led to further evaluation or change in the medical program of specific patients. Transtelephonic monitoring of cardiac rehabilitation exercise sessions at home and at remote hospitals appears safe and is attractive because not all patients have access to supervised exercise programs; this exercise assessment helps to maximally use highly trained cardiac rehabilitation personnel.