http://battlefield.wikia.com/wiki/Hardcore
Battlefield
Hardcore mode is present in Battlefield 3, acting similar to the Hardcore mode in Battlefield: Bad Company 2. Players can select hardcore-mode servers from Battlelog or the in-game server browsers on consoles, just as players can select infantry-only servers.
The Hardcore option reduces HUD elements and reduces the health of players, just as in Battlefield: Bad Company 2.