To evaluate the usefulness of telephonically-monitored home exercise in patients within two weeks postcoronary bypass surgery, we randomly enrolled 46 male patients in a 12-week home program of either short walks or bicycle ergometry. Home exercise was done five times weekly and monitored both before and immediately after three times weekly. New arrhythmias or conduction disturbances were detected in 18 of 23 (78 percent) of the bicycle group and in 20 of 23 (87 percent) of the short walk patients. New symptoms developed in three patients, two from the short walk group and one from the bicycle group. Two bikers and one walker developed elevated blood pressure; all were referred to physicians and were successfully managed. Electrocardiographic abnormalities led directly to diagnostic and therapeutic intervention in nine of the 46 patients-four bikers and five walkers. There were no complications such as ventricular tachycardia or ventricular fibrillation. Technically clear telephone rhythm strips were obtained from patients calling both locally and long distance.