Part: Part Twelve - Heads-Up

Three-betting heads-up

Pre-flop
Heads-up • Blinds 400 / 800Pot 2,800 (3.5 BB)BBA♣9♦● 20,000 (25 BB)YOUto actBTN● 20,000 (25 BB)Opponentraises 2,000 (2.5 BB)D

Heads-up. The button raises to 2,000 and you're in the big blind with A♣9♦.

Heads-up, button raises; you hold A♣9♦ in the BB. Best?

WhyThree-bet. A-9 offsuit is a strong heads-up hand, well ahead of the button's wide opening range. Three-bet for value and to seize the initiative - flatting lets him realize equity in position, and folding a hand this strong heads-up is far too tight.
What happensYou three-bet; the button folds or continues as an underdog.  Re-raise wide heads-up.
Heads-up you three-bet a wide, aggressive range - an offsuit ace is a clear value three-bet against the button's wide opens, and it grabs the initiative.

Three-bet wide heads-up for value and pressure - strong-ish hands like an offsuit ace are ahead of the button's wide range.