Now is a good time to clear-up TDA Rule #26 BUTTON IN HEADS-UP. In heads-up play, the small blind is on the button and acts first (pre-flop). I think that pre-flop needs to be added.
The dealer always deals away from the button...so in heads-up, the first down card goes to the BB. Pre-flop the betting action begins with the SB (on the button), having first option of folding, calling the BB, or raising. After the flop, the first betting option begins as normal so, the Button is last to act on the last three betting rounds.