Background: There are few studies regarding the role of oxidant status (OS) in children with congenital heart defects. We believed that CHD has led to increased levels of oxidative stress and inflammation and decreased antioxidant potential. This study aimed to investigate the oxidative status and its impact on the heart in infants and children with congenital cyanotic and acyanotic heart diseases. Methods: This case control study was carried out in cardiology Unit, Pediatrics department in Zagazig University Hospital from April 2017 to October 2017. 90 infants and children were included in the study, their age ranged from 2 months and 4 years they were divided randomly into three groups. Group 1: 30 children with cyanotic congenital heart defect, group 2: 30 children with acyanotic congenital heart defect and group 3: 30 healthy children as control group. All patients were evaluated clinically and investigated for routine laboratory in addition to Oxygen saturation measurement by pulse oximeter, Serum malondialdehyde and Echocardiography using Two-dimensional and M-mode measurements were obtained. Results: There was high statistical significant difference among three studied groups regarding oxygen saturation, which was normal in control group and lower in patient group and levels of Serum malondialdehyde, was highest among cyanotic heart defect group. Conclusions: Children with congenital heart diseases are susceptible to oxidative stress especially in those with cyanotic congenital heart diseases reflected by significant decrease of Partial Pressure of Oxygen and significant increase of Serum malondialdehyde (MDA) in cyanotic group when compared with the other 2 groups.