BACKGROUND: The pulmonary impairment in patients with bronchoconstriction induced by eucapnic voluntary hyperpnea(EVH) goes beyond the respiratory system, also impairing autonomic nervous modulation. This study aimed to evaluate the behavior of cardiac autonomic modulation in young asthmatics with and without EIB after the EVH test. RESEARCH DESIGN AND METHODS: A cross-sectional study design using 54 asthmatics(51.9% female), aged between 10 and 19 years, investigated with the EVH test. Forced expiratory volume in one second(FEV(1)) was measured at 5, 10, 15, and 30 min after EVH. Heart rate variability(HRV) measures of time were assessed pre and 30 min-post EVH. The diagnosis of Exercise-Induced bronchoconstriction with underlying clinical asthma(EIB(A)) was confirmed by a fall in FEV(1) >/=10% compared to baseline. RESULTS: Thirty(55.5%) asthmatics had EIB(A). Subjects with EIB(A) have reduced mean of the R-R intervals in relation to baseline until 15 minutes after EVH. Individuals without EIB(A) had increased parasympathetic activity compared to baseline(rMSSD) from 5 min after EVH(p < 0.05). This parasympathetic activity increase in relation to baseline was seen in individuals with EIB(A) after 25 minutes (rMSSD = 49.9 +/- 5.3 vs 63.5 +/- 7.2, p < 0.05). CONCLUSION: Young asthmatics with EIB(A) present a delay in the increase of the parasympathetic component after EVH when compared to asthmatics without EIB(A).