Sexual arousal causes an increase of blood flow into the penis which, when trapped, creates an erection for sexual activity. For some men, there is not enough natural blood flow for an erection, or the natural trapping mechanism allowing the erection to be maintained does not function properly. When the clear plastic cylinder of the vacuum device is placed over the penis, the attached vacuum pump causes blood to be drawn into the penis, causing an erection. Once the full erection is achieved, a special ring if placed at the base of the penis thus maintaining the erection. The ring must be released after sexual activity. The vacuum device is an FDA approved therapy, and is often favored by older patients not wishing to undergo more invasive therapy.