Routine heel blood was taken from the control group. At the same time, the behaviors of newborns were recorded on camera throughout the procedure. At the end of the study, the camera recording was watched and scored by two midwives who had training in the Neonatal Pain Scale.

The newborns in the experimental group listened to the recorded heart sounds of their mothers for 1 minute before the heel blood procedure, during the procedure and for 1 minute after the procedure. At the same time, the behaviors of newborns were recorded on camera throughout the procedure. At the end of the study, the camera recording was monitored and scored by two midwives trained in the Neonatal Pain Scale.

Heart sounds of the newborns' own mothers were recorded on the voice recorder with the help of a hand doppler device. This sound was listened by the newborns in the experimental group during the heel blood procedure.

The Newborn Infant Pain Scale (NIPS) was used. NIPS: Scale Lawrence et al. (1993) was developed to evaluate the behavioral and physiological pain responses of preterm and term infants. The scale consists of five behavioral factors (facial expression, crying, arousal, arm and leg movements) and one physiological (breathing pattern) factor. The crying factor is given 0-1-2 points, the other factors are given 0-1 points, and the total score is between 0-7. A high score indicates greater severity of pain.