A blue new born presents with cyanosis. The X–ray chest reveal oligaemic lung field and normal sized heart. Most likely diagnosis is –
Ebstein's anomaly
Pulmonary atresia
Transposition of great arteries
Tetralogy of fallot
The findings in this newborn are
Cyanosis at birth
Oligaemic lung .fields
Normal sized heart
Lets see each option one by one
Ebstein anomaly - It can be easily ruled out as there is marked cardiomegaly in it.
Transposition of great vessels- There is cardiomegaly and plethoric lung fields see in it. So ruled out.
Now the real confusion - between PA and TOF.
TOF - in TOF there is oligaemic lung fields and normal sized heart but usually cyanosis is not present at birth.
 
Nelson states -  "Often cyanosis is not present at birth. but with increasing hypertrophy of the right ventricular infimdibulum and patient growth, cyanosis occurs later in the 1st year of life. But some cases may present with cyanosis at birth."

a Pulmonary atresia -

The child is cyanotic at birth
There is pulmonary oligaemia
But the heart is of variable size (from small to enlarge)