Sildenafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow easily. 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. Those hoping to explore more natural and safe ways to improve sexual sensations may want to first explore topical solutions. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. An inherited eye disease that affects the retina. If you become pregnant while taking sildenafil, call your doctor. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often.In fact, a recent review of studies found that some counterfeit drugs contained a very high, dangerous level of sildenafil that far exceeded a typical . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. . Products and services Erectile dysfunction: Viagra and other oral medications By Mayo Clinic Staff Medicines that you take by mouth are called oral .