Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. This can happen if you are sick with fever, diarrhea, or vomiting; sweat a lot; or do not drink enough liquids. Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist. Sildenafil comes as a tablet and suspension liquid to take by mouth. Click here for an email preview. Ask your pharmacist for a list of the ingredients.Sildenafil (Viagra) is a phosphodiesterase-5 (PDE-5) inhibitor. PDE-5 is a protein in your body that breaks down the molecules that normally cause an erection. When it blocks PDE-5, sildenafil (Viagra) helps an erection occur by allowing certain muscles in the penis to relax and the penis to fill with blood. Sildenafil (Viagra, Revatio) is a moderately priced drug used to treat erection problems in men. It is also used to treat pulmonary arterial hypertension, a serious heart and lung condition. This drug is more popular than comparable drugs. It is available in generic and brand versions.  · Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men. Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women. Do not take Viagra while also taking Revatio. Warnings.