The diving response involves reflex bradycardia, apnoea and peripheral vasoconstriction and is known to exist in human infants. The response diminishes with increasing age and has been reported to disappear by the age of 6 mo. This study was performed to analyse the physiological events during natural diving of full-term healthy infants and describe how these events alter with maturation. Thirty-six infants were studied during diving exercises in infant swimming. All of the infants who participated showed an immediate decrease in heart rate when submerged. On average, the heart rate decreased by 25% (range -% to -%, p <). The bradycardia was sustained during the dive and for some seconds afterwards. The response was often followed by a tachycardia as the bradycardia ceased. A decline of reflex bradycardia was observed with increasing age (p = ), but the response was still clearly evident in infants over the age of 6 mo.