The expansion picks up where Wings of Liberty and is the second part of a trilogy. It will include additional units and multiplayer changes as well as continuing the campaign. The expansion to the campaign will add approximately 20 new missions focusing on the zerg species.
Beta testers for the expansion will be invited by Blizzard. The group of testers will begin with players who were involved in testing Patch 1.5, pro gamers and members of the press. That group will expand to additional players over time.
In order to have a chance to participate, gamers must be opted in for beta testing on Battle.net. Under the Account Management section of Battle.net, potential players need to check their Beta Profile Settings to make sure they are opted in. This does not guarantee entry into the beta but does give gamers a chance at being invited.
Blizzard also plans to give out more chances to enter the beta via the StarCraft community. Fansites and community personalities will provide additional opportunities to participate in the beta.
The beta will only be for the multiplayer experience of Heart of the Swarm.
While details for the campaign portion of Heart of the Swarm have been revealed by Blizzard, information on the changes coming to multiplayer have been scarce. The developer previously said the expansion will add seven new multiplayer units and remove three, but exact modifications have changed as tweaks to the expansion have been made.
StarCraft II: Wings of Liberty released in 2010 and sold over a million units in its first day of release.
No official release date for Heart of the Swarm has been announced, but Blizzard says the expansion is already complete. The team will be working on some fine tuning and polishing before it is released.