Side Effects Along with its needed effects, a medicine may cause some unwanted effects. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Push the plunger of the syringe, then insert the tip into the bottle while holding the bottle upright on a flat surface. If you are taking sildenafil to treat erectile dysfunction, you should know that it does not cure erectile dysfunction or increase sexual desire. Also tell your doctor if you have or have ever had pulmonary veno-occlusive disease PVOD; blockage of veins in the lungs ; a stomach ulcer; heart, kidney, or liver disease; a heart attack; heart failure; angina chest pain ; an irregular heartbeat; a stroke; chest pain; high or low blood pressure; high cholesterol; a bleeding disorder; blood circulation problems; blood cell problems such as sickle cell anemia a disease of the red blood cells , multiple myeloma cancer of the plasma cells , or leukemia cancer of the white blood cells ; conditions affecting the shape of the penis e. Angina severe chest pain , unstable or Arrhythmia irregular heartbeat, within the last 6 months or Blood vessel problems eg, aortic stenosis, idiopathic subaortic stenosis or Heart attack within the last 6 months or Heart failure or Hypertension high blood pressure or Hypotension low blood pressure or Retinal disorders eye problem or Retinitis pigmentosa an inherited eye disorder or Stroke within the last 6 months —Should not be used in patients with these conditions. Click here for an email preview.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. SILDENAFIL (sil DEN a fil) treats erectile dysfunction (ED). It works by increasing blood flow to the penis, which helps to maintain an erection. This medicine may be used for other purposes; ask your health care provider or pharmacist if you have questions. COMMON BRAND NAME (S): Viagra. Advertisement.  · 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.