Quote from elkpark
I don't have a source (too lazy to look one up), but I remember reading when Viagra first came on the market that it was originally developed/researched as a hypertension drug -- but so many of the male subjects in the clinical trials kept commenting on how much their sex lives had improved that Pfizer figured, well hey, there are tons of HTN drugs out there, but no one else has a drug that fixes your, umm, "sex life," so it would probably be much more profitable for them if they marketed it for that instead (and the rest is history...
So it does make sense.
You're on the right track.
Pfizer was experimenting with drugs that would promote blood flow to the heart, and at first they wondered if the mens' increased sexual function was due to improved overall circulation. This turned out not to be the case, and it really didn't work that well for the heart circulation.
I have filled more than one prescription for women who experienced sexual dysfunction after menopause or hysterectomy. When they call in their refills, they always preface it with, "You'll probably laugh at me, but....." No, I won't.
As for Viagra's discoverers getting a Nobel Prize, it wasn't because of the sex thing but because it led to additional discoveries regarding the nitric oxide cycle, which is believed to play a role in things like Alzheimer's, cancer, strokes, and the overall aging process.