How soon does viagra (sildenafil) begin to work?

About 20 minutes. Viagra (sildenafil) does not begin to work immediately, it has to be absorbed from your stomach, enter the blood stream and reach the penile blood vessels. This usually takes 20 - 30 minutes.
Viagra (sildenafil) Viagra (sildenafil) should be take on an empty stomache 1 hour prior to activity.