Background During bradycardia pacing in Ventritex Cadence (Models V-100 and V-110) implantable cardioverter-defibrillators, amplifier gain is maximal and oversensing and false tachyarrhythmia detection have been reported. Newer Ventritex devices (Cadet, Model V-115 and Contour, Model V-145) have a modified automatic gain control that may minimize oversensing. Methods and Results We prospectively studied 50 patients (22 with Cadence, 28 with Cadet or Contour). Electrograms were evaluated for oversensing during bradycardia pacing. The bradycardia pacing refractory period required to prevent oversensing of T waves of paced beats and the time and number of beats required to achieve minimum gain after cessation of pacing were assessed. The bradycardia pacing refractory period could be left at its default setting of 350 ms in only 15 (30%) of 50 patients. The mean bradycardia pacing refractory period required to avoid oversensing of paced T waves was 386 ± 32 ms. During pacing, oversensing of nonpaced T waves was seen in 12 (24%) devices, with similar incidence in Cadence devices (18%) and Cadet and Contour devices (29%, p = not significant). The time and number of beats to achieve minimum gain after pacing were longer in Cadence devices (19.0 ± 4.5 vs 4.6 ± 1.2 sec; 21.3 ± 3.3 vs 5.0 ± 0.4 beats, both p < 0.001). Conclusions The incidence of oversensing at maximum gain is similar in both types of devices, but more rapid changes in autogain levels in the newer devices may reduce the likelihood of false tachyarrhythmia detection. (Am Heart J 1998;136:658-63.)