Apart from 10-max and 6-max, a lot of sites also offer heads-up tables nowadays. You might not necessarily choose to sit down at one of them, but I think it's important for every player to develop a good heads-up game. Every player will, sooner or later, find themselves in a heads-up situation, and because heads-up play is so much different than normal poker, it will take some thinking before finding the right general strategy for these matches. Furthermore, you might be forced to sit down at an empty cash table every now and then if there are no good games available, and before this table fills up, you might have to survive a couple of rounds of heads-up poker.
It is a whole different way of playing: the fewer players there are at the table, the more often you will be in the blinds, which makes it even more important to defend your blinds and steal your opponents' blinds. This is so essential in heads-up play that, if you don't do it right from the start, you will end up losing a lot of money straight away. This is because you are forced to post a blind every hand, and against an opponent with a certain preflop raise percentage from the small blind (also the button in heads-up), you will have to defend a certain number of hands to avoid your opponents' investment becoming profitable straight away, purely based on fold equity.
Imagine a player raising every hand when sitting in the small blind (assuming the small blind is half the big blind and a preflop raise is the size of the pot, 3BB). Every time he does this, he invests 2.5BB to win 1.5BB. When just looking at the preflop situation, a player will have to win 62.5% of the time to break even (62.5x he wins 1.5BB = 93.75BB, 37.5x he loses 2.5BB = 93.75BB). This means that if you raise every hand in the small blind, your opponent will have to defend his blind 37.5% of the time (or compensate by playing profitably postflop and out of position) in order to not lose money on this play, and most players don't even come close to that number.
As you can see already, heads-up is usually a very loose game. Playing profitably out of the small blind/button with loose play isn't hard, but doing this out of position becomes a lot more difficult. Most regular/aggressive players will raise 75% of their hands from the button in a heads-up game, and against most opponents it's not difficult to defend more than 30% of your hands profitably. But to find out your heads-up winrate, you obviously need a lot more than just your stats against a SB open raise. Folding to a raise gives you an EV of 0, and you can compensate a lot by playing the hands that you do play profitably. Furthermore, you're in the SB position half of the time, which makes it easy for you to slope the big blind.
OK, so principally it's correct to raise any two cards from the button, and in the big blind it greatly depends on the opening range of your opponent. If he is aggressive and raises 75% or more of his hands on the button, you will have to defend around 25-30% of the time. How often and with which hands you chose to re-raise or just flatcall depends on his post flop game and how he reacts to re-raises.
In general, the more aggressive an opponent is postflop, the less you want to be sitting at the table with a deep stack. It is much easier to become a target of selective aggression if you only invest a small percentage of your stack preflop. Often you will need a very strong hand in order to play back at your opponent in these cases, while in re-raised pots the money is often in before you know it with hands like top-pair. So therefore, you want to re-raise more against players you play aggressively postflop. You hereby reduce the disadvantage from being out of position, while at the same time taking over the role as the aggressor, forcing your opponent to react.
It is also very important to know how your opponent reacts to your re-raises. If he often folds then you can re-raise him with a polarized range of hands. With this I mean that your range consists mainly of very strong and very weak hands. Since your opponent folds a lot, a call by him would indicate him holding a strong hand, which means you might even be better off holding a hand like than . If, however, he calls a lot of your re-raises, he will also have a lot of marginal hands in his range, so it is better to re-raise with than .
It all becomes more difficult if your opponent often 4-bets. If both of you are playing 100BB stacks, it isn't hard to decide which hands are good enough to go all-in with against his 4-bet range. In heads-up games, however, you often sit deeper than 100BB, which makes it more difficult to play back at his regular small 4-bets, as you often have too much money in front of you to make going all-in a profitable move. Your investment is larger in relation to the dead money that you can win, and his call range will be tighter, which decreases your equity if he does call. Sometimes you can just call against small 4-bets, but that would then be sort of floating. 4-betting ranges are often always polarized, in which case you don't call with the aim to hit the flop, because you have already invested such a great deal of your stack preflop, but rather to find out whether or not you are up against the 'bluff-section' of his range.
The size of the re-raise is also something that requires some thinking. You obviously don't want the size of your re-raise to give away any information about your hole cards, so the right thing to do is to re-raise the same amount with every hand. If you re-raise aggressively, which is the correct move in most heads-up matches, the best thing to happen with most of your range would be for your opponent to fold. You are playing a wide re-raising range mainly on fold equity, and the larger your re-raise, the bigger the chance that your opponent will fold (unless your re-raise is too big, in which case it might become profitable for your opponent to 4-bet shove). Then again, your investments are increasing too, so you need to find a balance between your betsizes and find the right relationship between fold equity and the size of your re-raise.
With stack sizes of around 100BB I would advise to keep your re-raises at around 10% of your total stack. With re-raises of more than 4x the original raise, your opponent would have to fold around 73% of the time to make your play profitable, and that would be the highest fold-to-3-bet percentage I have ever heard of in a heads-up game. Many aggressive players will often 4-bet in position with stacks of more than 150BB, and if they turn your 12BB re-raise into a 26BB 4-bet, it will be very difficult to defend yourself against this move with those stacksizes. You can avoid these situations by reducing the sizes of your 3-bets and just flatcall instead.
You can also experiment a little with the sizes of your opening raises. If, for example, you only raise to 2.5BB instead of 3BB, you risk less money to take down the pot, and force your opponent to play more hand. If he doesn't do this, you will lose half a big blind less every time he does play back at you, and you will still win 1.5BB every time he doesn't play back. You can also use this as a sort of defensive adjustment if you are having a hard time coping with the amount of re-raises and/or the size of his re-raises. He then wins less whenever you fold to his re-raise and you don't have to adjust your preflop open range.
The disadvantage of this style of play is that the pot stays relatively small. It is true that your position-advantage increases when the relation between stacksize and potsize increases. In other words: the smaller the pot in relation to the stacks, the more options you have to exploit your position. However, we're not playing to create the biggest possible edge on our opponent in every hand, we're playing to win as much money as possible. By increasing the size of the pot when in position, you are minimizing your edge per pot and increasing the variance, but there is more money in the pot every time you have the advantage of position.
So it sounds like you should actually open raise more than pot-size, but because the stacksizes are then relatively small in relation to your preflop raise, your 5BB raise can just be re-raised to 12BB, while little changes in terms of your implied odds when compared to a 3BB raise and a 10BB re-raise. The odds for your opponent, on the other hand, do change. In the first example he is risking 11BB to win 6BB and in the second example he is risking 9BB to win 4BB. Therefore, against most players this is only recommendable if the stacks are a little deeper, as you can call more often preflop against the small re-raises from your opponent.
Then there are a lot of opponents that don't raise often enough but call a lot when out of position. These are mainly weak players, against whom you can use this concept. This article was more about playing heads-up against aggressive opponents, with a lot of preflop pot-size raises in position. While this will be the case against most thinking players, it is of course always nicer to play against a fish. Playing against these players requires a whole different strategy than when playing against an aggressive opponent who plays back at you. You might think that because they call more, you can't play as aggressive. Well, the exact opposite is the case. Players who don't play on fold equity(aggression), but are actually hoping to hit their hand should be handled with even more aggression, as they will miss far more often than actually hit a strong hand.
Especially preflop these players will make a lot of mistakes. The larger the stacks, the less important preflop hand selection becomes, so by raising more you achieve two things. First of all, you make the stacks less deep in relation to the pot, resulting in your opponent winning less if he does hit. Furthermore, you get value while he is still willing to put money in the pot (preflop), to then win the pot when he is less willing to put money in the pot (postflop).
When in position, you will now have a new option: raise his limp. Good players will hardly ever limp the button, because it is so difficult to defend against an aggressive button opener. Weaker players will regularly limp on the button, and the frequency at which I raise his limp depends solely on the fold equity I believe to have with this bet. There is not much point in building up a big pot here with a bad hand instead of doing so when I am in position. Even against fish who only try to hit their own hand it can be hard to compensate for the disadvantage of being out of position. You might feel tempted to raise his limp here because limpers are often weak, but his limp is already better for you than the alternative. If he does just raise, you will have to fold most of your hands, and you can still raise most of the hands you would play anyway for value.
To say you should raise any 2 cards on the button against any player is a little exaggerated. In some cases the chance of a re-raise will be somewhat higher than normal, solely because of the game flow. If you have just opened the last 5 buttons in a row and then get 85o, this is a great time to just fold, after which you can open again with a hand like 83o, even though this hand is worse than the hand before. In heads-up matches, the game flow becomes a lot more apparent to players compared to when playing 6-max tables, something you always need to bear in mind. If you want your opponent to fold, then check out whether or not you have been active during the past couple of rounds. The circumstance under which your opponent will fold his hands the most is if your aggression goes unnoticed, or if they are involved in a big hand on another table.
As you can see, heads-up poker is a completely different kind of game and requires different adjustments in order to keep playing your A-game. Luckily your opponent will have to do the same, and if you manage to do it better than he/she does, you will be able to make use of this very fast, because the game is structured in a way that there is almost always action preflop and postflop. The next time I will discuss some postflop heads-up theory, which again is very different when compared to 6-max postflop poker. Made hands are worth a lot more and you can use completely different lines than you usually would. But more about this next time.