The Fortress Frenzy map sees players fight for control of a small island, where the only way on or off is via six bridges on either side of the isle.
The development team has also expanded the mission system, introducing new ways to earn Valour and Experience Points, and added Treasure Chests, which offer random rewards on killing enemies.
Starting today and lasting until July 1, players who log onto the game will receive two party packs, which include a Battlefield Heroes birthday shirt, a tricycle emote that lasts for three days and a Treasure Chest Key.
The party packs - one of which is Royal, the other National - can be downloaded by visiting the game's official website and clicking the 'Rewards' section under 'My Stuff'.
In the three years since its launch, Battlefield Heroes has attracted more than two million registered users - a number that has swelled to 12 million, according to a new trailer - and was targeted by LulzSec hackers.
Two UK members of the hacking group have today admitted that they helped carry out cyber attacks on high-profile websites.
Their court case has been adjourned until July 12 while the Director of Public Prosecutions decides whether the men should stand trial.
Watch the Battlefield Heroes third year birthday trailer below: