Heart of the Swarm did not sell quite as quickly as Wings of Liberty but has still had a successful launch.
Starcraft 2: Heart of the Swarm has managed to shift 1.1 million copies worldwide in just two days, according to Blizzard.
The 1.1 million in sales are made up of both physical and digital copies, although Blizzard has not stated how this figure was split between the two.
Launched on March 12, Blizzard also revealed that its launch day event broadcast online clocked up a further 1.1 million viewers, with the number of concurrent viewers peaking at 125,000.
In a further coincidence, another 1.1 million viewers tuned in to last weekend's Major League Gaming winter championship Heart of the Swarm tournament, with a peak of 157,000 concurrent viewers. The tournament was won by previous 2012 fall championship winner Lee 'Life' Seung Hyun, who collected the $25,000 grand prize.
The first Starcraft 2 release, Wings of Liberty, managed to break the 1 million mark by the end of its first day on sale, reaching 1.5 million in sales by day two.
Heart of the Swarm is the first major expansion to Starcraft 2 and features a zerg-focused campaign and has added new units to all three races in the popular multiplayer component of Starcraft 2. Despite being labelled as an expansion, it still features a lengthy single player campaign that picks up the story from where Wings of Liberty left off and has made substantial changes to the balance of the multiplayer.
The final Starcraft 2 instalment will be the Protoss-focused Legacy of the Void, which is yet to receive an official release date. Starcraft 2 game director Dustin Browder has however stated that they will be doing their best to reduce the time between expansions with this one.