Viagra affects the muscles in the genitalia area making them relaxed so that there won’t be any tension that stands in the way of erection. When extra tension is gone the active ingredient of Generic Viagra – sildenafil – starts working in the direction of widening the blood vessels in the penis. They are needed to be widen to let enough blood enter them so that the level of blood pressure can rise and make the penis erected. This is how Viagra works and does it perfectly well in 30-60 minutes after its pill having been taken. One pill is absolutely enough for the following 24 hours so there is no need to double the dose.