If you ever need emergency medical treatment for a heart problem, the healthcare providers who treat you will need to know when you last took sildenafil. Most patients receive a prescription for 50 mg of oral sildenafil, taken as needed approximately 1 hour before sexual activity. Do not press on the plunger of the syringe. If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. Consider starting at a dose of 25 mg in patients with hepatic dysfunction e.swelling in your hands, ankles, or feet; shortness of breath; seizure (convulsions); or. a light-headed feeling, like you might pass out. Common Viagra side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; abnormal vision (blurred vision, changes in color vision) runny or stuffy nose, nosebleeds;. 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 in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . Like Viagra, certain forms of sildenafil are approved to treat ED in males* ages 18 years and older. For example, sildenafil mg, mg, and mg tablets are approved for this use.