Consider this a friendly reminder to go double check your Battle.net account to be sure you're opted in for the StarCraft II: Heart of the Swarm multiplayer beta. While currently limited to pro gamers, shoutcasters, press, and Arcade contest winners, Blizzard will be expanding the pool of players before long.
According to the company, "Beta testers are chosen according to their system specifications and other factors, including recent StarCraft II activity (and an element of luck), when selecting individuals during each round of invitations. Our goal is to have a wide variety of players and system types."
While you technically don't need to own StarCraft II: Wings of Liberty to participate, not having a copy won't exactly help your chance of scoring a beta key. If all else fails, be on the lookout for giveaways on community sites.