Blizzard have announced the closure of the Heart of the Swarm public beta. Don't panic, it's not immediately. It is however only weeks away on the 1 March (you may panic now, if that is your wont). The private beta will continue till the game's launch on 12 March, however.
More details below.
The news came through a blog post on Battle.net which stated simply that "We’re pleased to announce that, in preparation for the launch of StarCraft II: Heart of the Swarm, the public beta test will close on March 1. We’re incredibly thankful for the feedback and data our testers have produced throughout the beta, and we hope that all testers continue to practice, prepare, and pursue XP levels in the beta through the end of February."