Well, unless you experience some sort of stimuli/stimulus, you are not going to experience random hard ons while walking through the gym, after taking viagra/cialis or a combination of the two. There still has to be something to excite you down there. The pills alone will not make you hard.
What the pills will do is increase blood flow, which is why some guys will take 5 to 10 mg of cialis before working out, to increase muscle pumps (blood flow to the muscle). Now, if you are sexually aroused, yes, your erection can be more immediate and more intense. But I have taken both of the above as both a PWO and pre-fuck-session, and I have never had an issue with getting a random erection unless sexually aroused/stimulated (either mentally or physically).
Now, Melanotan II / PT-141 on the other hand, that stuff produced "out of nowhere" arousal!!!
