[Note: This post is being updated because Fatal Hearts is on Daily Discount at BFG for $2.99 on September 22nd 2010, and the links needed fixing]
Fatal Hearts information has been posted at
Casual Game Guides
It's not quite a walkthrough, but it does have directions for each puzzle, pictures that go along with the explanations, and cheat codes to skip the puzzles.
You're probably still better off going to the game forums where you can ask other players for advice, and many questions have already been answered.
Someone's also made a video showing some of the puzzle solutions here
If you're interested in story-based games like this, you should also check out Date Warp or this blog's Visual Novel category!