If you are having trouble achieving or maintaining an erection during sexual intercourse, you may be suffering from a common condition called male impotence. This condition is also called erectile dysfunction, but it usually be successfully treated by taking a medication called Viagra. Technically, Viagra works by inhibiting an enzyme known as PDE-5. The drug relaxes muscles in the penis and increases blood flow to that area. This enables men to achieve longer and harder erections. However, Viagra must be taken in conjunction with sexual stimulation in order to be effective. It is recommended to take Viagra approximately one hour before engaging in any type of sexual activity.