We have evaluated a patient-actuated transtelephonic monitoring system (TTM) in order to determine its ability to document the cardiac rhythm at the time of symptoms; results have been compared to a simultaneously recorded 24-hour Holter Monitor (HM). Forty patients submitted an average of 15.6 TTM recordings/patient over a 7-day recording period. Twenty-six patients reported significant symptoms during the period of study: 11 had demonstrated arrhythmias, and these were documented by HM alone in one, by TTM alone in four, and by both HM and TTM in six. In 15 patients, no arrhythmia was seen during symptoms. HM alone was useful in excluding arrhythmia as a cause for the symptoms in two patients, TTM alone in six patients, and both in the remaining seven patients. Cumulative diagnostic usefulness in evaluating the significance of symptoms potentially attributable to arrhythmia is summarized: HM alone useful in three patients, TTM alone useful in 10 patients, and both HM and TTM useful in 13; TTM was significantly more useful than HM (χ2 = 3.69; P < 0.05). Of note is that six patients had significant arrhythmias during asymptomatic periods, including VPC's (four), severe sinus bradycardia (one), and rapid atrial fibrillation (one). In these few patients, both techniques appeared equally able to document asymptomatic arrhythmias. These observations demonstrate that TTM carried out over a 7-day period is superior to a 24-hour Holter monitor recording in its ability to establish the significance of symptoms potentially attributable to arrhythmia, and appeared equally sensitive to HM in demonstrating periods of asymptomatic arrhythmia. TTM can therefore be considered a simple, accurate, and useful technique for arrhythmia surveillance in the symptomatic patient. © 1979.