Methods Patients of ES with age greater than or equal to 18 years and weight greater than or equal to 30 kgs in World Health Organisation (WHO) functional class II and III attending our congenital clinic were invited to participate in the study. Informed written consent was taken from all the patients before screening procedures were initiated for the study. A detailed clinical examination and non-invasive testing including electrocardiogram, chest X ray, pulmonary function tests (to exclude associated restrictive/obstructive lung disease) and echocardiography(including contrast echo if required for demonstrating right to left shunt) were conducted. Patients with simple congenital heart defects (atrial septal defect > 2cm, ventricular septal defect > 1cm and aortopulmonary communications > 0.4 cm) with echocardiographic evidence of right to left shunt were included. Medical therapy and clinical condition of the patients had to be stable for 3 months prior to screening. Patients on treatment with prostanoids, endothelial receptor antagonists (ERA), PDE-5 inhibitors or any other vasodilators with in 1month prior to screening were excluded. A systemic pulse oximetry (SpO2) between 70% and 90% at rest in room air and a baseline 6 minute walk test(6MWT) distance between 150 and 450 meters were required for inclusion. Eisenmenger physiology was confirmed by cardiac catheterization as mean pulmonary artery pressure > 40mmHg, pulmonary capillary wedge pressure < 15mmHg and pulmonary vascular resistance >10 wood units/m2. Oxygen study was also done in selected patients to diagnose reversible pulmonary arterial hypertension(PAH) and such patients were excluded. Patients were also excluded if they were in WHO class IV, were in congestive heart failure or had PCWP > 15mmHg,had left ventricular ejection fraction <40%, atrial fibrillation, patent ductus arteriosus, complex congenital heart defects, restrictive lung disease(total lung capacity < 70% of predicted), obstructive lung disease ( forced expiratory volume in 1 second [FEV1] < 70% of predicted with FEV1/ Forced vital capacity [FVC] < 60%), previously diagnosed coronary artery disease requiring nitrate therapy, abnormal biochemical profile and hypersensitivity to PDE- 5 inhibitors. Left and right heart catheterization was done in eligible patients as described in our preliminary observational study. Calculation of pulmonary and systemic blood flow(Qs), PVR and SVR was performed using the Ficks equation and assumed values of oxygen consumption according to age and gender of patient. The study was conducted according to the most recent amendments to the Declaration of Helsinki and in adherence to good clinical practice guidelines. The trial was approved by the National Drug Regulatory Authority (DCG) and the ethical committee of our institution.