How does Viagra work?

During sexual stimulation, nitric oxide (NO) is released in the corpora cavernosa (two cylinders of spongy erectile tissue in the penis). The nitric oxide activates an enzyme called guanylate cyclase, increasing levels of a smooth-muscle relaxant known as cyclic guanosine monophosphate (cGMP). Smooth muscle acts involuntarily -- the conscious mind has no control over its actions. This kind of muscle is located in blood vessels, intestines, the stomach, and other areas. When Viagra (sildenafil) is tossed into the equation, it inhibits the effect of phosphodiesterase type 5 (PDE5) and enhances the effect of NO. Normally, PDE5 degrades cGMP. With sildenafil present, the increased levels of cGMP cause smooth muscle relaxation. Consequently, blood can flow into the corpora cavernosa more easily. In a normal erection, these two cylinders hold 90% of the blood that flows into the penis, with the balance going to the corpus spongiosum, a smaller cylinder containing the urethra.

Interestingly, this plays a role in one of Viagra's more unsual side effects. Some men who take this drug develop a bluish cast to their vision or have difficulty telling blue from green. Sildenafil is selective for PDE5, which means it has a greater effect on that particular phosphodiesterase than it does on others. In fact, it is 4,000 times more selective for PDE5 than for PDE3, which is responsible for heart muscle contraction! Unfortunately, it is only 10 times more selective for PDE6, an enzyme found in the retina and involved in phototransduction.


* Prescribing information for Viagra: http://www.pfizer.com/download/uspi_viagra.pdf
* Pretty much what is stated above, but with a nice, colorful diagram: http://health.howstuffworks.com/viagra5.htm
* Phototransduction: http://wolfstone.halloweenhost.com/TechBase/litadv_AdvancedLightingConcept.html#HowDoRodsAndConesWork

EDIT:
As per Relsqui's request, a "paraphrase for laymen":

Viagra causes smooth muscle relaxation, allowing blood to easily flow into the penis. Sometimes, Viagra will make your vision blue.

here you can get all the information you want. very detailed and yet understanable!
http://health.howstuffworks.com/viagra.htm

Pharmacist: Very well. Yes, it works well.

Customer: Can I get it over the counter?

Pharmacist: If you take two.

Ask the dozens of girls who are sore!!

Viagra makes YOU work :-))

My brother said great

Who Cares?

i dnt knw

it creates a higher pressure of blood pressue to the penis

wots the difference between the blue viagra and the blue viagra and does it work with amphetamines in your system

what is the difference between blue viagra and green viagra and does it work if you have amphetamines in your system

First you become old and rich. Then you divorce your wife. Then you find some young hot girl that just wants your money. Then you take Viagra. Then you do stuff in bed with the girl. Then you overhear the girl and her real boyfriend laughing at you as she is counting all the money she will get when you die.