Draw a card and take 2 damage.
Life Tap is a Warlock class Hero Power. Its effect is to draw a card and take 2 damage.
A very powerful ability. In CCGs the ability to draw more cards than your opponent is always extremely powerful, and this allows Warlocks to always maintain said advantage over their opponents. While there is the drawback of losing 2 life, this ability is often used in aggro decks to draw more cheap Minions that can be played to end the game quickly, before your opponent has a chance to capitalise on the fact that you have lowered your own Health. The only thing to watch out for is to not underestimate perhaps how much damage your opponent could do next turn, with boosts as well as weapons etc., otherwise you could commit suicide in the game by using this ability. Also you will run out of cards faster than your opponent, so make sure you use the extra card drawing to win the game before it gets to the point where you have run out of cards.