The fourth expansion pack in the Battlefield 3 suite subtitled, Aftermath, will take place in the ruins of Tehran, having been recently decimated by the earthquake from the original game.
According to the new information listed on the official site, the expansion will feature four new multiplayer maps themed on the destroyed environment of Tehran. It will also feature "heavily modified military and civilian vehicles" (we're not sure what that means, either), as well as new assignments, dog tags, and an all-new game mode that has not been detailed yet.
The next DLC pack to arrive will be the awesome-looking Armored Kill which will be available for download in September. Aftermath is currently on track for a December release, and the final DLC "End Game" is still set for a "Winter" release. However, given that Aftermath is coming in December we're pretty doubtful End Game will hit before January at the earliest.