Sildenafil may be of benefit for selected patients with pulmonary hypertension associated with parenchymal lung and cardiac diseases. However the medium term benefits of this treatment for such patients is unclear. 16 consecutive patients with secondary pulmonary hypertension who had been on maximal appropriate therapy received Sildenafil 50 mg tds following assessment which included right heart catheter, 2D echocardiography and six minute walk test. Right heart catheterisation, 2D echocardiography and six minute walk test were performed after eight weeks treatment, at 12 months and at six monthly intervals thereafter. Baseline medications were continued. 16 patients with pulmonary hypertension associated with inoperable chronic pulmonary thromboembolism (6 patients), valvular heart disease (4), chronic obstructive pulmonary disease (3), idiopathic pulmonary fibrosis (2), and obstructive sleep apnoea (1) were studied. The age range was 42 to 81 (median 68) years and the period of follow up was 12 to 51 (median 22) months. Six minute walk increased significantly, p=0.002, from baseline to long term follow up. The improvement in 14 patients ranged from 14 m to 300 m with a percentage increase of 5% to 567% increase. In one patient there was no change and in one patient the six minute walk test fell as a consequence of progression of known arthritis. The mean pulmonary artery pressure was significantly reduced at long term follow up (p=0008). The pulmonary vascular resistance (PVR) fell in eleven patients, this reduction ranged from 0.2 woods units to 8.7 woods units (mean reduction 3.3 woods units). The percentage reduction in PVR ranged from 7% to 71% with a mean reduction of 43%. In five patients the pulmonary vascular resistance increased. 2D echocardiography showed a sustained improvement in right ventricular function in 11 patients. There were no deaths during follow up. Sildenafil may have a role for selected patients with pulmonary hypertension associated with cardiac and pulmonary diseases. The medication seems well tolerated and for some patients is effective within 8 weeks and results in a sustained long term improvement in haemodynamics and exercise capacity.