robE hit the nail on the head when he said
I doubt it was H because it cannot really reach your blood stream in decent quantities. H is broken down in your stomach into Morphene and then filtered in your liver before reaching your blood by then its almost all filtered out.
This is exactly why heroin taken orally would work as a potentator for MDMA.
While the effects of a small quantity of heroin taken orally are, in the main, of minimal effect, heroin (and morphine) taken orally are big time substrates of P450-3A4, which is a major pathway for amphetamines, and in the case of the methylated amphetamines, conducts a key transformation, that being N-demethylation.
In other words, normally a lot of MDMA becomes freebase d-MDA before having any effect. Heroin effectively blocks this, radically altering the effect of the MDMA alone, and then, of course, it has a little "loved-up" feeling of its own to add to the overall effect.
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And the Mission is the Mouse...