Heads-Up Cash Preflop: The Button Opens Wide

Heads-up cash is preflop poker with nowhere to hide. Every single hand you are either the button or the big blind, every hand starts with a raise-or-fold decision against exactly one opponent, and the ranges involved are wider than anything a 6-max player has ever been comfortable holding. The format looks chaotic from the outside, but the chaos is structured: it all flows from one positional asymmetry, and once you see how that asymmetry sets the button's range, the big blind's response, and the 3-bet war on top, heads-up preflop becomes a system rather than a brawl. This article walks through that system using the solved heads-up cash trees, from 40bb to 200bb.

The asymmetry that defines the format

Heads up, the button posts the small blind and acts first before the flop. That sounds like a disadvantage, and it is a small one, for exactly one betting round. In exchange, the button acts last on the flop, the turn, and the river, every time, in every pot that continues.

That trade defines everything. Acting last is the most valuable structural edge in poker: the button sees the big blind's decision before making its own on three consecutive streets, realizes its equity more fully, bluffs more credibly, and gets away from second-best hands more cheaply. The big blind gets one round of positional relief, closing the preflop action, and then pays for it across the rest of the hand. Because the same two players swap these roles every single hand, heads-up poker is really two alternating games: the button's game, built on pressure and position, and the big blind's game, built on defense and counterattack. Preflop is where both games are set up.

Why the button opens most of the deck

Fold the button and you surrender the blinds with no resistance; raise it and three forces work for you at once. First, there is only one opponent left to act, so the raise needs to get through just one range rather than the four or five that sit behind an early open at a full table. Second, the big blind is forced to play the entire rest of the hand out of position when it continues, so even the pots you do not win immediately are played on favorable ground. Third, there is already dead money in the middle: both blinds are posted before anyone makes a decision, and the button's own small blind is a sunk cost that improves the price on raising rather than folding.

Run those forces through a solver and the answer is a range that would look absurd in any other seat: the heads-up button profitably opens a huge share of all hands, folding only the true bottom of the matrix. This is not looseness for its own sake. Each of those raises is individually profitable given position and the price, and the hands that fold are the ones that lose money even with every structural advantage stacked behind them. The practical consequence for a new heads-up player is uncomfortable but liberating: most of the discipline you learned in ring games about hand selection does not transfer, and the discipline that replaces it is about what happens after the open.

Open sizing: 2.5bb short, 3bb deep

The solved trees are specific about how much to raise, and the pattern is the opposite of what many players assume. From 40bb through 100bb the button opens 2.5bb. At 150bb to 200bb the open grows to 3bb.

The logic is that position appreciates with depth. When stacks are deep, the button's last-act advantage applies to bigger pots across more meaningful decisions, so each hand played in position is worth more, and the button can charge more for entry while still holding a range advantage. Shorter, with less money behind, the leverage of position shrinks and a smaller open does the same work at lower risk. Compare this with 6-max, where the standard open is 2.5bb across most depths: the heads-up button is the one seat that sizes up as money gets deeper, precisely because it is the seat whose edge scales with it.

Sizing discipline matters more here than anywhere else because of sheer volume. The button open is the single most frequent action in heads-up poker, occurring in roughly half of all hands you play. A small sizing error in a rare spot is a rounding error; the same error on the button open is a tax on your entire session.

The big blind's defense problem

Facing a button open, the big blind's ring-game instincts all point the wrong way. The hand looks weak, the opponent raised, folding feels tidy. But the big blind closes the action, has already posted a full blind, and is being offered a direct price against a range that contains most of the deck. Against an opening range that wide, hands that are routine folds at a full table are comfortably ahead of average, and surrendering them hands the button an enormous, silent edge one orbit at a time.

So the solved big blind defends wide, through a mix of calls and 3-bets, and the folding region is small. The closest analog in ring games is the blind battle, where the same forces of dead money, wide ranges, and forced positional disadvantage apply in miniature; SB versus BB preflop ranges covers that spot, and heads up is that dynamic promoted from an occasional side plot to the entire game. The difference is intensity: the heads-up big blind faces this decision every other hand, against a wider range, with no other players to change the equation.

Defense is not passive. A big blind that only calls lets the button realize its positional edge cheaply on every flop. The counterweight is the 3-bet.

The 3-bet war: 4x standard, 3x at 200bb

The big blind 3-bets out of position, and the solved sizing reflects it: 4x the open at most depths, trimming to 3x at 200bb. The size is doing the same job that out-of-position 3-bets do in 6-max, where deep 3-bets run about 3.4x in position but 4.4x from out of position: when you will play the rest of the hand at a positional disadvantage, you charge more now, deny the button its cheap in-position flop, and push the pot toward sizes where preflop equity matters more than maneuvering.

The trim to 3x at 200bb is the exception that explains the rule. With that much money behind, bloating the pot out of position starts cutting the other way, because the reverse leverage of deep stacks punishes the player who builds a big pot without position. The solve keeps the pressure but moderates the price. Ring-game players can port a lot of intuition here from standard 3-bet theory, and 3-bet ranges in 100bb cash is the reference for that foundation, but heads up everything runs wider: the button opens more, so the big blind 3-bets more, with a value region reaching deeper into the matrix and a bluff region built from hands that block continues and play tolerably when called.

4-bets: 2.4x deep, all-in territory by 40bb

Facing the 3-bet, the button's counterattack is compact. Deep, the solved 4-bet runs about 2.4x the 3-bet, a small raise that reopens the action, applies maximum pressure per chip, and keeps the button's positional advantage alive for the streets where it pays. As stacks shorten the small 4-bet loses its room to work: by 40bb, 4-betting is effectively all-in territory, because the raise commits so much of the stack that the shove and the small raise have converged into the same decision.

This is the general depth pattern in miniature. Every raise in the tree needs stack behind it to function as a decision rather than a commitment, and each halving of the effective stack strips a level off the tree. At 200bb the heads-up game has opens, 3-bets, 4-bets, and still room for play; at 40bb the fourth bet is the stack.

Depth bends the whole tree, not just the sizes

Put the pieces together across the solved span, 40bb to 200bb, and heads-up preflop is not one strategy but a family of them. Deep, position is at its most valuable: opens are bigger, the 3-bet trims to keep pots controllable, speculative suited hands gain because there is money behind to win, and the button's edge is at its peak. Short, raw equity takes over from playability, the 4-bet fuses into the shove, and the game tightens toward confrontation. In between, every depth is its own mix, and the shifts are exactly the kind of thing feel gets wrong, because the sizes and boundaries move in ways that are patterned but not obvious.

That is the case for working from the solved trees directly rather than a single memorized chart. The heads-up game is solved deeper than 6-max, to 200bb, precisely because heads-up pots so often escalate and deep coverage is where the interesting divergences live. The cash preflop charts serve the full heads-up trees in the browser as live, interactive grids, so you can flip between depths and watch the tree reshape itself, which is the fastest way to internalize the pattern rather than one frozen slice of it.

The purest range war in poker

Heads-up cash strips poker down to the part most players never study: two ranges, one positional asymmetry, and a preflop war that repeats every hand. There are no tight early seats to hide in and no multiway pots to dilute responsibility. Every leak in your button strategy is taxed every other hand, and every fold the big blind should not make is a coin dropped in your opponent's pocket. That relentlessness is why heads-up specialists have historically been the strongest preflop players in the game, and why studying the format sharpens your blind-versus-blind and short-handed play even if you never sit a heads-up table professionally.

It is also why owning the actual solved trees matters more here than in any other format. The Cash Bundle includes the complete heads-up cash solves from 40bb to 200bb alongside the full 6-max trees, as range packs you buy once and own forever, and the same solves run as live charts in the browser viewer. The full library of range packs covers the other formats when you want them. However you study it, study it as a system: the button's width, the big blind's defense, and the raise war on top are one connected answer to one positional asymmetry, and once that clicks, heads-up preflop stops feeling like chaos.