The GameShark code for infinite HP in "Pokemon Emerald" is 8120241E8 03E7. The codes D8BAE4D9, A86CDBA5 and A5AFF3E4 unlock infinite money that can be used to buy maximum HP-ups.
GameShark offers many cheat codes for "Pokémon Emerald," including those that unlock fighting Pokémon, the ability to buy Master Balls and other rare items, the ability to walk through walls and even the ability to teleport to specific places in the world. Websites such as Super Cheats offer complete lists of these codes. As with all cheating devices, GameShark can corrupt save data, so make sure to have extra save backups if using a ROM.