Background: Congenital heart diseases which are dependent on the ductusarteriosus to maintain adequate oxygenation or systemic blood flow are termed as a critical congenital heart disease (CCHD). Delay in the diagnosis of CCHD is the major cause leading to morbidity and mortality in newborn infants. Clinical evaluation is likely to miss the diagnosis in first few hours of hospital stay after birth due to absence of signs and symptoms of CCHD.In the absence of clinical findings during early neonatal period, the best parameter that can be assessed is the detection of hypoxemia by pulse oximetry screening. Objectives: To record the value of Pulse Oximetry within 24 hours of birth and evaluate Pulse Oximetry as screening tool for early diagnosis of CCHD. Methods: Longitudinal descriptive study was conducted on total 700 intramural neonates, satisfying the inclusion and exclusion criteria, who were evaluated within 24 hours of birth with currently available pulse oximeter, after the Institutional Ethical Committee approval. The study was conducted over a period of 4 months. Part-A: Neonatal Case Record, Part-B: Pulse Oximetry Screening Record, Part-C: Clinical Examination Record, Part-D: Echocardiography Record. Results and Conclusion: Total 700 neonates were screened by pulse oximeter with consecutive sampling method. 4 (0.57%) subjects were detected to have positive screen and the diagnosis was confirmed by echocardiography. Study revealed that Pulse Oximetry Screening can be an important primary screening tool in routine neonatal care for early detection of Critical Congenital Heart Diseases particularly in rural setup.