<prompt> Differential cyanosis occurs inPDATGATricuspid stenosisVSD  <response>: Differential cyanosis is present when the preductal right upper extremity oxygen saturation is higher than the postductallower extremity saturation.ETIOLOGY:- PDA with reversal of shunt.- Persistent pulmonary hypeension of the newborn.Reverse differential cyanosis:In this condition only the upper pa of the body is cyanosed and the lower pa is pink.ETIOLOGY:PDA TGVsevere pulmonary hypeensionPDATGVpreductal coarctation of the aoa 