Seems to me it's a waste having a hardon you can do pushups with if you have zero libido, which Viagra does nothing for. But I guess you can fake it a few times a week for the missus' sake.
Dostinex (to lower the dreaded prolactin levels, which cause impotence) or stacking Winstrol (to block progesterone effects, which trigger raises prolactin levels) will help with impotence and libido issues.