Whispers of the Old Gods is Hearthstone's third expansion, launched April 26th, 2016. Featuring 134 new collectible cards, this sinister expansion revolves around the dark influence of the Old Gods, ancient and unspeakably evil creatures that have long lain hidden, imprisoned in the dark places of the world millennia ago. Despite their imprisonment, these shadowy beings' influence can be felt in every corner of Azeroth, twisting and corrupting any who hear their maddening whispers. With an army of followers performing forbidden empowerment rituals, the tentacles of these massive horrors are growing rapidly toward the light, eager to bring their own kind of excitement to the sunlit kingdoms and merry taverns of Azeroth
Source: The Game Website.