Physical inactivity and low resting heart rate variability (HRV) are associated with increased coronary heart disease incidence. In the Whitehall II study of civil servants aged 45-68 years (London, United Kingdom, 1997-1999), the strength of the association of moderate and vigorous activity with higher HRV was examined. Five-minute recordings of heart rate and HRV measures were obtained from 3328 participants. Calculated were time domain (standard deviation of NN intervals) and high-frequency-power measures as indicators of cardiac parasympathetic activity and low-frequency power of parasympathetic-sympathetic balance. Leisure-time physical activity (metabolic equivalent-hours per week) was categorized as moderate (>or=3-<5) and vigorous (>or=5). Moderate and vigorous physical activity were associated with higher HRV and lower heart rate. For men, linear trends of higher low-frequency power with increasing quartile of vigorous activity (304.6 (low), 329.0, 342.4, 362.5 (high); p < 0.01) and lower heart rate with increasing quartile of moderate activity (69.6 (low), 69.2, 68.9, 67.8 (high); p < 0.05) were found. These associations remained significant after adjustment for smoking and high alcohol intake. For men whose body mass index was >25 kg/m(2), vigorous activity was associated with HRV levels similar to those for normal-weight men who engaged in no vigorous activity. Vigorous activity was associated with higher HRV, representing a possible mechanism by which physical activity reduces coronary heart disease risk.