In pulmonary hypertension it works by relaxing blood vessels in the chest. Take sildenafil exactly as directed. For treatment of erectile dysfunction: For oral dosage form tablets : Adults up to 65 years of age—50 milligrams mg as a single dose no more than once a day, 1 hour before sexual intercourse. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. Ask your doctor if you have any questions. · Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where this enzyme works. About sildenafil (Viagra) Sildenafil is a medicine used to treat erection problems (erectile dysfunction). Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs). If you have erection problems sildenafil works by temporarily increasing blood flow to your penis when. Since Viagra is a brand-name medication, the price of Viagra is very high and may not currently work within your budget. Thankfully, a generic version of the popular medication .