Causes of cynosls-
Tetralogy of Fallot causes low oxygen levels in the blood. This leads to cyanosis (a bluish-purple color to the skin). The classic form includes four defects of the hea and its major blood vessels: Ventricular septal defect (hole between the right and left ventricles) Ref Davidson 23rd edition pg 455
TOF
PDA
Tricuspid atresia
Eisonmenger's complex
C.V.S