Contributing factors might include: (i) hypoxemia and acidosis during the intrauterine or the early postnatal period; (ii) restrictive oval fossa or foetal ductal constriction resulting from increased oxygen content in the pulmonary artery in foetuses with TGA; (iii) increased pulmonary artery wall thickness and muscularity with intimal proliferation; (iv) mediating pathways such as endothelin-1, prostacyclin-cGMP, nitric oxide-cAMP and vascular endothelial growth factor; and/or (v) clinically unrecognized pulmonary microthrombi [13, 15–17]. This evidence concerns the gene EDN1 and transposition of the great arteries.