If you've seen a "HeartGold GBA ROM" online, it is almost certainly:
If you own a modded 3DS, you can inject the DS ROM directly into your home screen using tools like NDS Forwarder . This is the closest you will get to a "native" handheld experience without dual-screen clutter, as the 3DS physically houses DS hardware inside.
The popularity
However, I understand you might be looking for one of these:
, which recreates the complete Johto and Kanto journey with modern features. Top Pokémon HeartGold GBA Recreations pokemon heart gold gba rom
Nintendo Pokemon: HeartGold Version & SoulSilver Cartridges Tested & Working Guarantee - Electronics
as a base to recreate the Johto region with modern features. Top Pokémon HeartGold GBA Recommendations If you've seen a "HeartGold GBA ROM" online,
Pokémon HeartGold and SoulSilver were officially released by Nintendo and Game Freak for the in 2009. They are technically incompatible with the Game Boy Advance hardware.