Sildenafil for Chronic Obstructive Pulmonary Disease (COPD) Associated Pulmonary Hypertension

Inclusion Criteria: * A mean pulmonary arterial pressure of 25 mmHg measured by right heart catheterization. * A diagnosis of COPD-associated pulmonary hypertension, implicating that no other potential cause of pulmonary hypertension is present. * Stable COPD, defined by no subjective alterations of symptoms or use of short acting beta-antagonists for minimally six weeks. Any exacerbation resulting in admission to hospital or other contacts to a physician must have ceased for at least 6 weeks before entering the study. * Age \> 18 * Informed written consent. * Reliable anticonception for fertile women. Exclusion Criteria: * Rheumatic disease limiting walking capacity. * Exacerbation in COPD during the study. * Age\>80 years * FEV1 \< 25 % of predicted. * Allergy towards contents of sildenafil or placebo tablets. * Fall in blood pressure of \> 30 mmHg systolic or \>20 mmHg diastolic after intake of the first dose of trial medication. * Fall in peripheral saturation of \> 5% after intake of the first dose of trial medication. * Treatment with nitrous vasodilators or aminophyllamines.