This question already has an answer here:
One of the plot points of Iron Man 2 is that Tony Stark is being slowly poisoned to death by the palladium that powers his chest arc reactor; and he can't just do without the reactor, because that is the only thing that prevents the shrapnel in his chest from entering his heart. Within this movie, the problem is resolved by creating a new arc reactor powered by a nontoxic unnamed element.
But then, at the end of Iron Man 3, Stark decides to undergo surgery to remove the shrapnel from his chest, thus eliminating his need for a chest arc reactor. Why wasn't this option entertained in Iron Man 2? I appreciate that the surgery might be risky, but if the alternative is death by palladium poisoning, you might be willing to take the risk (and that's not even counting the fact that Stark, being the genius he is, could have devoted time to devise ways to lower the surgical risk).