Several modalities have been proposed to reduce procedural pain in neonates. This study was conducted to determine whether heat of a non-human source might help with pain management in infants. Methods: In this clinical trial, 40 full-term healthy neonates in their first hours of life were randomly divided into two groups of intervention and control. The control group was put under a radiant warmer using the servo-controlled method for four minutes and the temperature was set to 35.5°C. The

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... rvention group was put under the servo-controlled mode with the temperature of 35.5°C for two minutes, then two minutes in manual mode with 100% power. Vitamin K injection was performed. The severity of pain in infants was measured by an independent observer by means of Neonatal Infant Pain Scale (NIPS) before the injection, 20 seconds during the injection, as well as 60 and 120 seconds after the injection. The difference in pain score was compared between the two groups using Chi-squared test, repeated measures analysis of variance, and independent t-test. Results: The two groups were similar in terms of gestational age, birth weight, Apgar score, and maternal age. The mean of NIPS scores was 2.9 in intervention group and 4 in the control group during injection, which was significantly different (P=0.001). No significant difference was recorded in skin temperature and pain scores before and after injection. Conclusion: Heat application during intramuscular injection can relieve procedural pain in neonates.