Mild side effects possibly. Not a stonking erection so hard you could knock a hole in a brick with it. Viagra helps you maintain an erection for satisfactory sex it won't turn you into a pornstar. In my experience anyway, I suffer from heartburn, headache, blue-vision (but only if I take 100mg as opposed to 50mg - don't overdo it by the way!). It can give me the shits!
I have taken Cialis as well and it was much better - longer lasting, fewer side effects, stonking erections - much better than I get on Viagra! However, it's too expensive for me. These days I'm only prepared to take licensed drugs - generic Viagra from Asda I'm OK with but I'm not going to import some dodgy unlicensed Cialis copy from China any more.