['Our objective was to investigate the effect of a long-term moderate exercise program on cardiac autonomic nervous system (ANS) activity in healthy children.', 'Three hundred and five children aged 6-11 years participated in a 12-month school-based exercise training program (130-140 bpm, 20 min/day, 5 days/week). Cardiac ANS activities were measured using heart rate variability (HRV) power spectral analysis in resting conditions. Following the first measurement, 100 children from the lowest total power (TP) HRV were chosen as experimental samples and the same number of age-, height-, and weight-matched controls (CG) was randomly selected from the remaining children.', 'In the low group (LG), all the frequency components of the HRV were significantly increased after the training period, whereas only low-frequency power was augmented in the control group (CG).'] Does moderate physical exercise increase cardiac autonomic nervous system activity in children with low heart rate variability?