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Objectives— We sought to determine the usefulness of ambulatory 24-hour Holter monitoring in detecting asymptomatic pacemaker (PM) malfunction episodes in patients with dual-chamber pacemakers whose pacing and sensing parameters were proper, as seen in routine post-implantation follow-ups.This aspect has not been widely discussed so far.Methods and results— Ambulatory 24-hour Holter recordings [HM] were performed in 100 patients with DDD pacemakers one day after the implantation. Only asymptomatic patients with proper pacing and sensing parameters (assessed on PM telemetry on the first day post-implantation) were enrolled in the study.The following parameters were assessed: failure to pace, failure to sense (both oversensing and undersensing episodes) as well as the percentage of all PM disturbances. Despite proper sensing and pacing parameters, HM revealed PM disturbances in 23% of the patients. Atrial undersensing episodes were found in 12 patients and failure to capture in 1 patient. T wave oversensing was the most common ventricular channel disorder (9 patients). Malfunction episodes occurred sporadically, leading to pauses of up to 1.6 s or temporary bradycardia, which were, nevertheless, not accompanied by clinical symptoms. No ventricular pacing disturbances were found.Conclusion— Asymptomatic pacemaker dysfunction may be observed in nearly 25% of patients with proper DDD parameters after implantation.Thus, ambulatory HM during the early post-implantation period may be a useful tool to detect the need to reprogramme PM parameters.