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The authors present a case report of a patient with an implanted VDD pacemaker whose postoperative ECG revealed sinus bradycardia, showing the heart rate remarkably lower than the programmed lower rate limit. Upon assessing some pacemaker manufacturers' mechanisms to set the lower rate limit in VDD mode, it was found that they can be classified into four types. The mechanisms are based on keeping atrioventricular (AV) synchronous pacing in VDD mode or maintaining the lower rate limit in VVI mode. AV synchronous pacing results in producing an actual heart rate which is lower than the programmed lower rate limit. The classification also depends on whether the pacemakers are operating on either atrial-based or ventricular-based lower rate timing. Therefore, the actual heart rate can be lower than the programmed lower rate limit, depending on the VDD pacemaker model.