Although mild increase in pulmonary vascular resistance following intracardiac repair of tetralogy of Fallot is often seen in the early postoperative period, it usually subsides without any sequel. Persistent severe pulmonary artery hypertension after total correction is rare. We report a child with tetralogy of Fallot and Down's syndrome, who developed severe pulmonary hypertension and low cardiac output syndrome following an intracardiac repair, which was resistant to specific pulmonary vasodilators and increasing ionotropes. The post correction echocardiogram suggested an intact ventricular septal defect patch, no residual gradient across the right ventricular outflow tract, with free pulmonary regurgitation. The child had a poor outcome. A postmortem biopsy revealed histopathological signs of pulmonary hypertension.