Respuesta :

An erection that will not go away (priapism). 
S
udden vision loss in one or both eyes 
Sudden hearing decrease or hearing loss.
Viagra is used to stifle the messengers of cGMP. So that a male can sustain an erection.

Side effects can include headaches, stuffy nose, impaired vision, sensitivity to light, indigestion, and the possibility of a (painful)long lasting erection