More than half of all pacemaker systems currently implanted function rate-adaptively. Our objective was to determine which patients benefit from rate-adaptive pacing in terms of improvement in maximum performance and aerobic capacity. Thirty patients with implanted accelerometer-driven, rate-adaptive pacemakers were examined ergospirometrically and patient symptom-limited while walking on a treadmill. The patients were divided into three groups depending on the intrinsic heart rate achieved during maximum workload: Group I achieved < or = 90 bpm, Group II achieved 90 to < or = 110 bpm, Group III achieved > 110 bpm. Group I demonstrated a significant increase (p < or = 0.01) in maximum oxygen uptake from 16.4 +/- 5.6 ml/kg/min with fixed-rate pacing to 23.2 +/- 11.1 ml/kg/min (+41.5%) with rate-adaptive pacing. At the anaerobic threshold, oxygen uptake significantly increased (p < or = 0.01) from 11.8 +/- 2.7 ml/kg/min to 15.7 +/- 5 ml/kg/min (+33.1%). Group II showed an increase in maximum oxygen uptake from 23.3 +/- 5.4 ml/kg/min to 25.3 +/- 4.9 ml/kg/min (+8.5%, p < or = 0.05) as well as an increase in oxygen uptake at the anaerobic threshold from 15.9 +/- 2.6 ml/kg/min to 18.1 +/- 2.9 ml/kg/min (+13.8%, p < or = 0.05) with rate-adaptive pacing. Group III demonstrated no significant difference between the two pacing methods (from 25.6 +/- 9.4 ml/kg/min to 25.9 +/- 9.3 ml/kg/min and from 15.8 +/- 5.5 ml/kg/min to 16.3 +/- 6 ml/kg/min). No difference in maximum oxygen uptake and in oxygen uptake at the anaerobic threshold was evident between the three groups when paced rate-adaptively (n.s.).(ABSTRACT TRUNCATED AT 250 WORDS)