Deal 1 damage to ALL minions.
The way to tell seasoned warriors from novice ones: the novices yell "wheeeee" while whirlwinding.
 How to get
Whirlwind x 2 are a reward for raising a warrior to level 6.
Whirlwind will deal damage to ALL minions on the field, including friendly minions. A good early card to have as a way to wipe out low health taunt minions. You can also use the area damage to boost the damage of minions that have Enrage such as Amani Berserker and Tauren Warrior when the opposing player does not have any small creatures on the board to activate the effect on. This allows for some big hits opposing champion or clearing some of the larger minion targets on the board without having to take a turn to swing at something else first.
This card combos well with Battle Rage to damage everything on the board then draw a card for every character of yours still alive.
This card works extremely well with Frothing Berserker. For example, if there are 5 minions on the board (including the Berserker), playing Whirlwind will cause Frothing Berserker to gain 5 Attack, instantly making it a very powerful card.
Whirlwind is a melee-range area of effect warrior attack. The warrior attacks all enemies within 8 yards in a whirl of steel, causing a percentage of weapon damage to each enemy. Whirlwind is an effective way of dealing damaging to multiple targets, and is only desirable when attacking groups of enemies. Unlike its appearance in Hearthstone, it does not deal damage to friendly targets.
Early in the game's development, this card had the effect "Deal 1 damage to all enemies. If you have a weapon, +1 damage. If you are below 12 Health, +1 damage." This was eventually simplified to the card's current text, due to excessive complexity for players trying to learn and calculate the effects of playing the card.
- Hearthstone Panel BlizzCon 2013. (2013-11-09).