Conflicting data are published regarding the influence of acid gastroesophageal reflux on the heart rate. In this study, heart rate was monitored simultaneously with esophageal pH in 50 infants with symptoms suggestive of gastroesophageal reflux disease (frequent vomiting and regurgitations). The data of 25 preterm infants (born at 28-36 6/7 weeks) were compared to those of 25 term infants (born after 37 weeks of gestation). However, both groups were investigated at identical postconceptional age of 47-49 weeks. Not one significant bradycardia (heart rate < or = 80/min during > or = 10 s) was recorded, although 71 "relative bradycardia episodes" (heart rate < or = 80/min during > or = 5 beats) were detected, none lasting for > 5 s. Although the number of infants with relative bradycardia episodes did not differ between groups, the relative bradycardia episodes occurred more frequently in some preterm infants (53 episodes in preterm infants vs. 18 in term babies). Acid gastroesophageal reflux episodes were observed in 46 infants (92%). Neither the number of reflux episodes nor their duration was different in both groups. Simultaneous relative bradycardia episodes and acid reflux episodes were observed in three of 23 preterm and two of 23 term infants (NS). It is concluded that in a population of preterm and term infants with symptoms suggestive of a moderate gastroesophageal reflux pathology, investigated at comparable postconceptional age, most reflux episodes are not time-related to changes in heart rate.