A more drastic, option for treating ED is a penile implant. This is not usually considered unless there is a clear medical cause for ED that is unlikely to improve. The penile prosthesis is usually inflatable. It has two cylinders that are placed in the penis and connected by tubing to a reservoir of fluid, which is located under the groin muscles. A pump is also added, under the skin of the scrotum. To inflate the penis implant, a man presses on this pump in the scrotum. The pump then transfers fluid from the reservoir into the cylinders in the penis, inflating them and causing an erection. Similarly, a valve returns the fluid to the reservoir and deflates the penis. Although a penile prosthesis does not change the sensation in the penis, once the prosthesis has been implanted, most men cannot get an erection naturally ever again. Despite this, up to 90 percent of men are satisfied with the results of their penile prosthesis.