OBJECTIVE: To assess cardiac autonomic modulation, measured by short-term frequency domain analysis of heart rate variability (HRV), in children with asthma. METHODS: We conducted an observational study at a tertiary care teaching hospital. The sample consisted of 119 children aged 7 to 15 years with asthma and 56 age-matched healthy controls. Frequency domain HRV measures included low-frequency (LF; 0.04-0.15 Hz), high-frequency (HF; 0.15-0.4 Hz), and LF/HF ratio. The LF and HF components were expressed in both absolute values of power (ms(2) ) and in normalized units (nu). RESULTS: Compared with healthy controls, asthmatic children had significantly higher value of HF (nu) (mean +/- standard deviation: 45.9 +/- 14.6 vs 40.7 +/- 13.6; P = .02), and lower values of LF (nu) (54.1 +/- 14.6 vs 59.3 +/- 13.6; P = .02) and LF/HF ratio (median, interquartile range: 1.12, 0.82-1.88 vs 1.59, 1.02-2.08; P = .03). We did not find significant differences between children with persistent and intermittent asthma, and between children with well-controlled and partially-controlled or uncontrolled asthma, in terms of HRV measures. CONCLUSIONS: Children with stable chronic asthma may have a cardiac autonomic imbalance with a possible enhanced parasympathetic modulation, as assessed by short-term frequency domain analysis of HRV. Neither asthma severity nor asthma control was significantly associated with HRV measures, but the study did not have enough power to draw a firm conclusion on this point.