 Eisenmengers syndrome presents as a severe clinical picture of polymorbidity that constitutes a great burden at the individual as well as the familial and social level. The combination of critically increased pulmonary vascular resistance, progressive pressure load of the right ventricle and disturbance of pulmonary gas exchange result in long-term polymorbidity. The objective of this study is to provide evidence of improvement of patients exercise tolerance as well as general conditions by treatment with oral sildenafil as a specific pulmonary vasodilator. 