Follow your doctor’s orders or the directions on the label. If you are taking sildenafil for PAH, take the missed dose as soon as you remember it. Remove the cap by pushing it down and twisting it counter-clockwise. If you experience chest pain, dizziness, or nausea during sexual activity, call your doctor immediately and avoid sexual activity until your doctor tells you otherwise. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. · Generic name: sildenafil (oral) [ sil-DEN-a-fil ] Brand names: Revatio, Viagra Drug classes: Agents for pulmonary hypertension, Impotence agents Medically reviewed . Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise .  · Descriptions Sildenafil is used to treat men who have erectile dysfunction (also called sexual impotence). Sildenafil belongs to a group of medicines called .