Abstract: Background:  One of the developmental supportive care interventions introduced to NICUs is auditory and tactile stimulation. Early exposure to auditory stimulation especially with maternal heartbeats, represents a unique source of sensory stimulation for premature infants. Purpose: To determine the Effect of Mothers' Heartbeats on Premature Infants' physical and physiological parameters. Research design: A quasi-experimental research design (study and control groups) was used to complete this study. Settings: The study was conducted in the Neonatal Intensive Care Unit at Damanhur National Medical Institution (DMNI) and the Neonatal Intensive Care Unit at Kafr Eldwar General Hospital, at El Beheira Governorate- Egypt. Sampling: A purposive sample of 60 premature infants from the previously mentioned settings were selected. Instruments: Two Instruments were used to collect the necessary data. Instrument one: Characteristics and Medical History of Premature Infants Assessment Sheet and Instrument two: Premature Infants Physical and Physiological Parameters Assessment Tool. Results: The Heart Beats (HB) Group exhibited significantly lower heart and respiratory rates p <0.001 and slightly lower temperatures p = 0.002 than the control group, with consistently higher oxygen saturation p <0.001. Also, maternal heartbeat exposure significantly positively affected weight gain and mid-arm circumference in the HB Group, with highly statistically significant differences p <0.001. Conclusion: Premature infants who heard their mothers' heartbeats had better physical and physiological parameters in the study group compared to control group. Recommendations: Auditory stimulation such as mothers' heartbeats needs to be incorporated into the care of premature infants in the NICU