One of the most powerful men in music claims Dwight Howard's failure in Houston was cardiovascular ... saying D12 would've needed a "heart transplant" to win a ring in H-Town.
TMZ Sports got James Prince -- you might remember him as the Houston rap god who got Steve Francis' chain back when it was jacked at a Sauce Twinz show last year.
We wanted to know from Mr. Prince what every Rockets fan wants to know regarding Dwight Howard's time in Houston ... what went wrong?
Check out the clip -- Prince -- never one to mince words (ask Diddy) -- keeps it pretty real about his feelings on Howard bolting for ATL ... basically calling Dwight's heart into question.
If you're expecting a response from Howard ... don't.