oxycodone is a derivative of thebane, a stimulative opiate. that is why it is much less sedating. some of it is metabolized into oxymorphone in the body, but not all of it.
heroin is broken down into morphine after a couple hours. sucks that heroin is so potent compared to morphine, so you build a tolerance real fuckin quick when you're usin the stuff often.
the highs? not alike at all. but to each his own. too much heroin and i'd go puke, but feel fine for the rest of the night. too much oxy, on the other hand, i'd be fucking miserable for the rest of the night, puking my guts out and feeling like shit. heroin is soooo much more enjoyable for sooo many reasons, the only downside is how sedating it is.