Objective To investigate the correlation between premature beats,atrioventricular block (AVB),heart rate variability (HRV) and age as well as gender among normal children.Methods One thousand five hundred and eighty-one cases of normal children from Beijing were divided into three age groups:3 to 6-year old,～ 10-year old and ～ 12-year old.All children were evaluated with both ECG and Holter to determine arrhythmia and HRV.The arrhythmia incidence and five time-domain values of HRV were analyzed according to age,gender and the existence of ventricular premature contractions.Results (1) Both ECG and 24-hour ECG monitoring (Holter) data showed that the average heart rate (HR),the slowest HR and maximum HR of normal children decreased with age,while PR interval and QTc interval increased with age.The correlation between age and the four indices were statistically significant (P ＜0.01),except the PR interval.(2) The positive rate of arrhythmia with Holter and ECG in normal children had statistically significant difference(x2 =4.810,P ＜ 0.05).(3) The incidence of premature contraction and Ⅰ ° AVB rised or fell with increasing age(P ＜ 0.05).Compared with 3 ～6-year age group,10-year and ～ 12-year old group had highly risk tendency in premature contraction(OR =1.31,2.04).(4) The five time-domain indices of HRV were increases with age.Each age group had statistically significant difference (P ＜ 0.01).(5) The five time-domain indexes of HRV in males were higher than those in females (P ＜0.01).(6) No significant differences were found with five time-domain indexes in children with or without ventricular premature contraction (P ＞ 0.05).Conclusions (1) HR of normal children decreases with age,but QTc interval increases with age.(2) The supraventricular premature contraction is the most common arrhythmia in normal children with Holter.(3) The occurrence of premature contractions increases with age,more obvious during the preadolescence.Ⅰ ° AVB occurs with age growth on a downward trend.Sex has no effect on the same arrhythmia.(4) HRV in normal children has age difference,suggesting that the pediatric cardiac autonomic nervous system (ANS) was immature.(5) The differences of HRV in sex were most significant during the preadolescence,which showed the developmental inconsistencies in cardiac ANS between male and female of preadolescence.(6) In the majority of normal children,the ventricular premature contractions were benign.