The present study was performed to investigate heart rate responses and occurrence of arrhythmias caused by various diving maneuvers and swimming in infants. Forty four healthy infants (mean age 2.5±1.1, mean ±SD) served on this study. Condition of telemetry electrocardiograph recording was 1) rest on the land and in the water, 2) diving, 3) swimming and 4) “pass in water (PW) ”. Moreover, diving styles was classified for five patterns by presence of body movement or expiration (Apneic not move diving, Expiratory not move diving, Apneic kick diving. Expiratory kick diving and Underwater swimming) . “Diving bradycardia” was observed during diving and PW, and the magnitude of heart rate reduction was grater in diving without body movement than diving combined with body movement. Presence of expiration did not influence on the level of bradycardia during diving. Any kinds of arrythmias was observed 13 out of 44 subjects. In premature contractions, supraventricular premature contraction (SVPC, 7 subjects) was observed more often than ventricu-lar premature contraction (PVC, 3 subjects) . Another arrhythmias observed was atrioventricular junctional rhythm (AVJR, 1 subject), atrioventricular junctional escaped beat (AVJEB, 3 subjects) and wandering pacemaker (1 subject) . The danger arrhythmias which is necessary to restrict on exercise or swimming was not observed in this study.