Developmental changes in the cardiovascular system could have an impact on risks associated with psychopharmacological interventions. Children may be more vulnerable to adverse cardiac events due to immaturity in autonomic control of the heart. These changes are incompletely understood and are characterized in this study. A consecutive series of 70 boys, aged 6-14 years, was recruited. Developmental variation in the autonomic nervous system was evaluated by assessing heart period variability (HPV), pulse, and blood pressure in response to orthostasis. Increased age correlated significantly with greater heart rate and diastolic blood pressure response to orthostasis. HPV at rest and in response to tilt did not significantly correlate with age. Boys with family histories of hypertension had a significantly greater blood pressure response to orthostasis. These findings suggest that developmental age-related changes in the sympathetic nervous system, as reflected by changes of pulse and blood pressure response to tilt, occur across this age range. Parasympathetic changes, as reflected by HPV, do not. In light of these findings, more research is needed on children's and adolescents' relative cardiac risk with psychotropic medications as opposed to adults'.