Ambulatory electrocardiographic monitoring was performed on 360 healthy children, from newborn infants to junior high school students. They were divided into five groups by age: group A, 63 newborn infants on the first day of life; group B, 50 infants aged 1-11 months; group C, 53 kindergarten pupils aged 4-6 years; group D, 97 primary school pupils aged 9-12 years; and group E, 97 junior high school students aged 13-15 years. The maximal and minimal heart rates were significantly greater in infants than in older children. Sinus arrhythmia was recorded in every child. One boy in group E had an episode of sinus arrest for three seconds without any symptoms. First-degree and Wenckebach type second-degree atrioventricular blocks were not detected in group A and group B, but were most frequent in group E, especially during sleep. Supraventricular premature contractions (SVPCs) were the most common type of arrhythmia detected in this study. More than half of the children had at least one SVPC per 24-h monitoring period, and there were many children with frequent SVPCs in group E. The incidence of ventricular premature contractions (VPCs) in children of groups A and E was rather higher than in the other groups. Ventricular tachycardia was not recorded in any child except one newborn infant who had a couplet of VPCs without symptoms. Each group had different types and incidences of arrhythmias. There was a rising incidence of arrhythmias with advancing age, except in the neonatal period.

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