Viagra

I wanna ask if someone knows why it´s possible to have sex, when using viagra but whitout using Viagra it´s dificult or mostly not possible. I did not thougt that Viagra cut help on this situation that we have after using fina. ???

My second problem is that i can not use Viagra, because of sideeffects. Do any here know any other alternatives than Viagra ?

Sorry for my bad English. English i not my 1. launghue.