Viagra (sildenafil citrate) is prescribed for certain cases of male impotence, namely - erectile dysfunction. This condition can be caused by a variety of factors, from psychological to purely physical. The effects of Viagra are based on increasing the blood flow into the tissues of the penis. That results in a fuller erection that goes away once the man has an orgasm - just like it normally happens. In some very rare cases patients on Viagra report priapism. This condition can be described as a prolonged and often painful erection that does not go away even after an orgasm is experienced. Since priapism is fraught with permanent damage to the tissues of the penis this symptom should be immediately reported to the local emergency room and the patient should be treated for this condition as soon as possible.