If it is not treated right away, priapism can permanently damage your penis sudden vision loss in one or both eyes. You need to be sexually excited for it to work. Tell your doctor or pharmacist if you are taking nitrates medications for chest pain such as isosorbide dinitrate Isordil , isosorbide mononitrate Monoket , and nitroglycerin Nitromist, Nitro-Dur, Nitrostat. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food. Please expect up to 4 to 6 weeks for reimbursement.Online buyers beware. Sketchy sites with catchy names abound: , and , for example. The people behind the sites often . 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 drug is more popular than comparable drugs. It is available in generic and brand versions. Generic sildenafil is covered by most Medicare and insurance plans, but . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 hour.