<prompt> A two-month-old infant is brought to emergency depament with marked respiratory distress. On examination, the infant has cyanosis and bilateral crepitations. Hea rate is 180min, respiratory rate 56min and the liver span 7.5 cm. The child had repeated episodes of fever, cough and respiratory distress since the time of bih. Cardiovascular examination reveals a grade III ejection systolic murmur in left para-sternal area and the chest X-ray reveals cardiomegaly with a narrow base and plethoric lung fields. What is the most likely diagnosis?Congenital methemoglobinemiaTransposition of great aeriesCystic fibrosisTetralogy of Fallot  <response>: - In the given case scenario, infant has features of hea failure, cyanosis with repeated episodes of pneumonia suggesting increased pulmonary blood flow. - These clinical features along with the chest X ray findings are suggestive of Transposition of great aeries. - ON X-RAY : Egg on side or Egg on string appearance is characteristic of transposition of great aeries Other options: Congenital methemoglobinemia: Inherited in autosomal recessive pattern Diagnosed by genetic testing blood tests CYSTIC FIBROSIS: Mutation in gene encoding for CFTR - Located on long arm of chromosome 7 Presents with recurrent bronchiolitis in infancy, recurrent lower resp tract infections, bronchiectasis, steatorrhea, pancreatitis azoospermia Diagnosed by presence of typical phenotype family history confirmed by high sweat chloride on atleast 2 occasions by identifying mutation in both copies of CFTR TOF: Doesnt present with cyanosis at bih. X-ray shows Boot shaped hea. 