Viagra acts by increasing blood flow to the affected areas (your junk). It can also cause increases in blood pressure and cardiac problems...and death. It can be a fun drug that can give a healthy make wood on demand for as many as eight hours. You do need to have sexual desire however. Furthermore, Viagra can mess with and damage your junk if you are not a person with ED. Those are the facts as I understand them, but I will not testify under oath. Normally, I can keep wood for ten straight hours, so I've never felt the need to try it. Good luck to you lesser men.