Congenital heart diseases may remain asymptomatic for days or weeks after birth. Early diagnosis of prenatally undiagnosed congenital heart diseases rests upon familial history of congenital heart disease and clinical signs such as cyanosis intrauterine growth retardation, tachypnea, excessive sweating, feeding difficulties, or abnormal cardiac auscultation. Hyperoxia test, blood gas determination, chest x-ray and electrocardiogram are the most useful complementary tests before the anatomical evaluation by the pediatric cardiologist. The initial medical management includes mechanical ventilation and oxygen supplementation, insertion of a good quality central or peripheral vascular line, correction of metabolic disorders, sedation, and prostaglandin administration in order to maintain the opening of the ductus arteriosus.