A five-day-old, full term male infant was severely cyanotic at bih. His chest X ray showed 'Egg-on -side' appearance. Prostaglandin E1 was administered initially and later balloon atrial septosomy was done which showed improvement in oxygenation. The most likely diagnosis of this infant is:
Tetralogy Fallot Transposition of great vessels Truncus aeriosus Tricuspid atresia