OBJECTIVE: To validate an incremental field walking test, the shuttle walking test, as a means of assessing pacing modes and to aid programming of rate responsive pacemakers. DESIGN: Three separate groups of patients were recruited. Reproducibility (n = 10) of the shuttle walking test was assessed by performing three consecutive tests. Comparison of the shuttle walking test with a 10 min walk was assessed in 20 patients. In the third group (n = 10) patients with rate responsive pacemakers were programmed to either VVI fixed rate 70 beats/min or VVIR with the optimal rate response to show the discriminative value of the test. SETTING: Pacing clinic in a regional cardiothoracic centre. PATIENTS: 30 patients with chronotropic competence and dual chamber pacemakers with varying functional capacity and 10 patients with rate responsive pacemakers. INTERVENTIONS: Continuous haemodynamic monitoring was obtained using an ambulatory nuclear monitor, the Capintec VEST. Two exercise tests either shuttle walking test or 10 min corridor walk. The shuttle walk is an incremental walking test conducted on a 10 m course where the walking speed is dictated by bleeps on an audio cassette. RESULTS: Reproducibility was demonstrated over three consecutive tests with mean (1 SD) exercise times of 7.6 (1.7) min, 7.7 (1.6), and 7.7 (1.7) min. During the shuttle walk the test patients walked for a mean of 8.3 (1.2) min producing peak relative cardiac outputs of 78 (21) end diastolic volume/min compared with 64.9 (17) end diastolic volume/min for the 10 min walk (P < 0.001); peak heart rates were 118 and 104 beats/min (P < 0.03) respectively. In the third group relative peak cardiac output was significantly greater in VVIR (70 (24) v VVI 52 (15) end diastolic volume/min) (P < 0.009) as were exercise times (VVIR 8.8 (1.3) min v VVI 8.1 (1.3) min) (P < 0.003). CONCLUSIONS: The shuttle walk is an easy test to administer, requiring little equipment. It produces a symptom limited maximal performance and will be a useful aid to pacemaker programming as it is reproducible and able to show differences in exercise capacity between pacing modes.