MP, Instant, 34
Possibly without justification, I had a vision that 4H on a 5-2 fit may scrape home if partner's Hearts are good enough. Personally I would not have bid 2H with North, but it is not the worst thing that GIB has ever been known to do, and some of you out there may disagree with me anyway on that point.
Where we came undone possibly is that the explanation attached to my 4H bid says 3+ Hearts. Given that on the previous round partner has promised 5+ of them, would I risk partner passing a non-forcing 3C bid if I had held 3+ card support? I think that I am showing precisely 2 card support (assuming that it is not a cue bid going slamming in diamonds). Either way, with such poor Hearts North should then know to pull.