ABSTRACTThe present study investigated the applicability of the Law of Initial Value (LIV) for heart rate (HR) responses evoked by a nociceptive stimulus in neonatal sleep states. Ten infants were tested during Quiet and Active Sleep. In concordance with the LIV there was a significant inverse correlation for allSs in Active Sleep between HR change and prestimulus HR values; the average correlation was ‐.76, the average slope ‐.48. In Quiet Sleep, which had a small prestimulus HR range, this relationship was significant only for someSs. Equating for prestimulus HR values, no significant difference existed in the magnitude of average HR response in Active Sleep vs Quiet Sleep. It was concluded that for nociceptive stimuli the initial HR value is a better predictor than the behavioral sleep state of the magnitude of HR response. It is suggested that the LIV depends largely on the modality and strength of the stimulus and the width of the prestimulus HR ra