Previous studies have shown that single-chamber sensor-driven pacing improves exercise tolerance for patients with chronotropic incompetence. However, long-term single-chamber pacing has a number of inherent problems that limit its usefulness. Although sensor-driven dual-chamber pacing largely obviates the problems inherent with single-chamber sensor-driven pacing, the physiologic benefit of dual-chamber sensor-driven pacing has not yet been demonstrated. Accordingly, the purpose of this study was to compare exercise-induced cardiac output for patients with chronotropic incompetence, after programming their pacemakers to either a simulated sensor-driven single or simulated dual-chamber mode. Cardiac output was measured noninvasively at rest and peak exercise using standard Doppler-derived measurements, obtained in a blinded fashion. At rest the Doppler-derived resting VVI and DDD cardiac outputs were 4.49 ± 0.3 L/min and 4.68 ± 0.3 L/min, respectively. At peak exercise, the DDD cardiac output was 5.07 ± 0.5 L/min, whereas the simulated activity VVI and DDD cardiac outputs were 6.33 ± 0.6 L/min and 7.41 ± 0.70 L/min, respectively. Analysis of variance showed that there was an overall significant difference in cardiac output from rest to peak exercise (p < 0.001). However, only the simulated activity DDD cardiac output was significantly different from its respective control value (p < 0.05). Thus this study shows for the first time that the addition of rate responsiveness to dual-chamber pacing results in a significant improvement in cardiac output for patients with chronotropic incompetence.