Our aim was to underline possible differences in heart rate and rhythm patterns between ambulatory and hospitalized children. Holter monitoring was performed on 264 healthy ambulatory children and on 112 children who were hospitalized for noncardiotoxic conditions. Maximal, mean and minimal heart rates decreased with age. Maximal heart rate was significantly higher in ambulatory schoolchildren and adolescents than in hospitalized ones. Sinus arrhythmia was noted on every recording. Some children had episodes of first- or second-degree atrioventricular block while sleeping. Supraventricular and uniform ventricular extrasystoles were common. The incidence of all types of arrhythmia and conduction disturbances was similar in ambulatory and hospitalized children. These data can be taken as a basis for the analysis of 24-hour electrocardiogram monitoring in ambulatory but also in hospitalized children.