Venous leak, medically known as veno-occlusive erectile dysfunction (ED) or corporo-venous occlusive dysfunction, is a condition in which the penis has difficulty maintaining an erection because blood does not remain trapped inside the erectile tissues for long enough. Normally, sexual stimulation causes increased blood flow into the penis. The erectile tissues expand, and the veins responsible for draining blood away from the penis become compressed. This mechanism helps maintain a firm erection. In venous leak, this trapping mechanism does not work effectively, allowing blood to leave the penis too quickly. As a result, a person may be able to achieve an erection but have difficulty maintaining it or may notice that the erection becomes softer during sexual activity. Venous leak can have several possible causes, including changes in the erectile tissue, vascular problems, diabetes, injury, pelvic surgery, and other conditions that affect penile blood flow or the veno-occlusive mechanism.