Like Vastness said, it really depends on what the bag is made out of. A small, 1g ziplock will most likely break open, either from the stomach acid eating away at the bag or the seal being compromised from the liquid and mechanical motions of your stomach and bowels as it moves through your GI tract. If stomach acid leaks into the bag, it will expand and eventually rupture, leading the contents spilling out. Luckily, if it is heroin, it wont be very bioavailable via this ROA, so depending on how much you ingested, you still might be ok if it does break. Swallowing bags unpredictable, all it takes is a tiny hole or gap or the wrong material to burst. Hope you are safe!