Objectives The purpose of this study is to evaluate the characteristics of autonomic nervous system in heart-weakened children via analyzing heart rate variability (HRV) compare to healthy children. Methods Among the children who have visited the department of pediatrics at OO oriental medicine hospital, the subjects were composed of 62 elementary school students without cardiac disorder, who have yet develop secondary sexual characteristics. Results 1. Mean HRT and SDNN of the heart-weakened group of children were lower than the healthy group, but with no statistical significance. 2. Heart-weakened children had higher LF norm and LF/HF ratio, but lower HF norm than healthy children. The rest of the Frequency Domain Index have no significant differences. 3. Heart-weak score showed a positive correlation with Mean HRT and LF/HF ratio. Conclusions Heart-weakened children had an imbalance in autonomic nervous system due to increase of sympathetic nerve activity and decrease of parasympathetic nerve activity.