Sildenafil Viagra. Bleeding disorders, history of or Stomach ulcer, or history of or—Chance of problems occurring may be increased. If you will be taking this medicine for pulmonary arterial hypertension, your doctor will want to check your progress at regular visits. If you need emergency medical care for a heart problem, it is important that your doctor knows when you last took sildenafil. Its effects often last for 4 to 5 hours. If you experience a prolonged or painful erection for 4 hours or more, contact your doctor immediately. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . 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 . The effects may be increased because of slower removal of the medicine from the body. Leukemia (blood related cancer) or. Multiple myeloma (blood related cancer) or. Sickle .