Twenty-four hour ambulatory electrocardiographic monitoring is a useful method to document dysrhythmias and to assess treatment response. Various studies have been done in the pediatric age-group to determine normal heart rate values. In this study we determined the heart rate and rhythm patterns of 25 healthy newborn infants whose ages ranged between 3-10 days (mean 6.5 days). There were 15 males and 10 females. The maximum heart rate in these infants was 175-231 beats/min (207 +/- 14), minimum heart rate 60-121 beats/min (93 +/- 16) and the average heart rate was 130-161 beats/min (143 +/- 9). Five infants (20%) demonstrated marked sinus dysrhythmia, seven infants (28%) had ventricular premature contractions, two infants (8%) had supraventricular premature contractions, and five infants (20%) showed junctional rhythm disturbance. The sinus pause did not exceed 1.2 sec and there was no evidence of atrioventricular conduction disorders, or supraventricular-ventricular tachycardia attacks. Our results were consistent with previous studies carried out in newborn infants. Dysrhythmias were detected during 24-hour ambulatory electrocardiographic monitoring in our study group. Since they were generally benign, they need no treatment.