Revatio 20 mg contains sildenafil citrate as the active ingredient. Sildenafil is also sold as Viagra for erectile dysfunction. In patients suffering from PAH, Revatio dilates the blood vessels and reduces pulmonary vascular resistance. Revatio 20 can be used with existing therapies in people who are not responding adequately to monotherapy. Sildenafil works by inhibiting cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type-5 (PDE5). PDE5 causes the degradation of cGMP in the pulmonary vasculature muscle cells. By inhibiting PDE5, Sildenafil increases cGMP in the muscle cells, thus resulting in relaxation.