Age, diabetes, hypertension, obesity, high lipids, smoking, drugs, heart disease, upright cycling for more than 3 hours a week can cause erectile dysfunction (ED) in males. Those who ride bicycles for more than 3 hours a week should do so in a reclining position and not upright position. A man is considered to have ED when he cannot acquire or sustain an erection of sufficient rigidity for sexual intercourse. Any man may, at one time or another during his life, experience periodic or isolated sexual failures. The term "impotent" is reserved for those men who experience erectile failure during attempted intercourse more than 75% of the time. Heart disease increases the risk for later ED; ED also may be an early warning sign of future heart disease. Men with erectile dysfunction without an obvious cause (e.g., pelvic trauma), and who have no symptoms of heart disease, should be screened for heart disease prior to treatment since there are potential cardiac risks associated with sexual activity in patients with heart disease. Eight of the 12 most commonly prescribed medications list impotence as a side effect and it is estimated that 25% of cases of ED are due to drugs. Depression, stress, or the drugs used to treat depression can result in ED. Neurologic causes include stroke, spinal cord or back injury, multiple sclerosis, or dementia. In addition, pelvic trauma, prostate. Surgery or priapism may cause ED. A less obvious, but of increasing importance, has been the possible association of ED with bicycling. Anything that places prolonged pressure on the pudendal and cavernosal nerves or compromises blood flow to the penile artery can result in penile numbness and impotence. Cycling-induced impotence, is primarily a problem of serious cyclists and has been reported to occur in Norwegian men competing in a 540 km bicycle race. The penile numbness is attributed to the pressure on the perineal nerves whereas the erectile dysfunction is thought to be due to a decrease in oxygen pressure in the pudendal arteries. Recreational cyclists, those who cycle for less than 3 hours per week and men who cycle in a reclining position avoid the sustained intense pressure on the penile nerve and artery and are less likely to experience sexual side effects. Continued cycling in a seated upright position can reduce the penile oxygen levels lasting 10 minutes.