A five day old, full term male infant was severely cyanotic at birth. Prostaglandin E was administered initially and later ballooned atrial septostomy was done which showed improvement in oxygenation. The most likely diagnosis of this infant is –

Transposition of Great vessels is a condition characterized by aorta arising from the right ventricle and pulmonary artery from the left ventricle. This results in complete separation of systemic and pulmonary circulation. Since systemic and pulmonary circulations are separate, survival depends on mixing of oxygenated pulmonary blood and deoxygenated systemic blood which can occur: At Atrial level              :                    Through ASD At Ventricle level          :                  Through VSD At Great vessel level     :                 Through Patent ductus arteriosus Oxygenation is normal in foetus but after birth as ductus arteriosus closes severe hypoxia occurs and in the absence of VS.D, or ASD child presents with cyanosis and tachypnea at birth.