In order to obtain reliable information about time-domain ECG parameters in Russian children and to analyse their links with physiological changes the Project "ECG screening of children and adolescents of the Russian Federation" was carried out in 2003-2008. Time domain ECG parameters were studied in the representative sample of 5387 healthy individuals aged 0 to 18 years. In each age group, lower and upper limits of the norm for heart rate (HR), P wave, PQ and QRS intervals were defined as 2nd and 98th percentiles of their distribution. The equivalent limits of QT interval duration were defined as its 5th and 95th percentiles. Relationship between time domain parameters of pediatric ECG and HR was analyzed as well as relationship of these parameters with sex and age. The most important differences from prior pediatric studies completed 30 years ago were obtained for the heart rate limits. Among children aged 0 to 3, there was a tendency toward lowering of age-specific lower limits and elevation of age-specific upper limits. At ages older than 3 years, there was a tendency toward lowering of both the upper and the lower limits of HR. The newly obtained 2nd percentiles of the heart rate were lower than the known lower limits in nearly all ages. This indicates the necessity for revision of criteria of bradicardia in children. The present study showed that 5th and 95th percentiles of QTc interval (Bazett's formula) varied between 340 ms and 465 ms and were not significantly dependent on children's age and only for ages under 13 also on sex. Results of the study allowed to build age-specific ranges of norm for the time domain ECG parameters presented in a tabular form.