Similar to Wings of Liberty, the briefing room is replaced with an interactive exploration of the Leviathan, an enormous Zerg breed which functions as a Bioship. The player plays from the perspective of Sarah Kerrigan, recently returned to her human form by Jim Raynor. The game has 20 missions in the campaign (plus 7 evolution missions which allows the player to upgrade its units), and continues the story from Wings of Liberty.

The expansion includes additional units and multiplayer changes from Wings of Liberty, as well as a continuing campaign focusing on the Zerg race, following Sarah Kerrigan in her effort to regain control of the swarm and enact her revenge on the Terran Dominion’s emperor, Arcturus Mengsk. Heart of the Swarm is the second part of a planned StarCraft II trilogy, with part three titled Legacy of the Void. StarCraft II: Heart of the Swarm is an expansion pack to the military science fiction real-time strategy game StarCraft II: Wings of Liberty by Blizzard Entertainment.