Brief periods of transtelephonic electrocardiographic transmission conducted at periodic intervals or during sporadic symptoms may provide an inexpensive and reliable alternative to extended ambulatory electrocardiographic tape recordings. Sixty-one patients were enrolled in a transtelephonic electrocardiographic transmissions program. In 51 patients with documented arrhythmias (group I), telephone electrocardiographic transmissions were used to monitor antiarrhythmic drug therapy. In 10 patients, telephone electrocardiographic transmission was used in an attempt to diagnose infrequent symptoms suggestive of arrhythmia (group II). Of the 650 telephone electrocardiographic transmissions received, 73 (11%) revealed a clinically significant event, whereas 577 (89%) did not show any significant disturbances of cardiac rhythm. Of the 61 patients entered into the program, 29 (48%) had a clinically significant event identified during 1 or more transmissions. In group I, transtelephonic electrocardiographic transmission prompted a change in therapy in 37% of the patients. Of the 10 patients in group II, clinically significant events were noted during telephone electrocardiographic transmissions in each patient. Assuming a yield of 1 clinically significant event detected per 10 telephone electrocardiographic transmissions and a similar yield on long-term ambulatory electrocardiographic recordings, use of telephone electrocardiographic transmissions offers a cost-effective means of following patients with significant cardiac arrhythmias who are receiving potent antiarrhythmic drugs. In addition, telephone electrocardiographic transmission is a suitable diagnostic technique for patients with infrequent symptoms suggestive of cardiac arrhythmias.