A new adventure and 31 cards. http://www.bit-tech.net/news/gaming/2015/03/09/hearthstone-blackrock-mountain-expansion-un/1
I used to be so scathing of CCG dismissing them as not 'true' gaming. However, I have become hopelessly addicted to Hearthstone due to the compelling mixture of strategy, maths, logic and a healthy dollop of luck. As such I look forward to this new expansion, it can seem pricey but the thought that went into Naxx, plus some good light humour, made it good value in my warped fragile mind!