I have tried several times sildenafil together with cannabis in having sexual intercourse with my partner. I've found that while cannabis has an effect of widely enhancng excitatory stimuli and the orgastic level up to a real climax, sildenafil is effective in having easily repeated intercourse without stop beacause of its effect in erection; so, while cannabis enhances the excitement and empowers libido, sildenafil cause a very long lasting erectile performance even after the ejaculaction.
I think that this combination may provoke very positive effects on sexuality, especially if you like to have a sex session quite out of the ordinary with your usual partner. Very, very exciting.