I know the question has been answered, but allow me to provide further info.
Most people call it Feralheart, which is the correct term, but there are other variations, such as FeralHearts, Feral-heart, Feral Heart, Feral Hearts and FH. Quoting xRubyx, it may be because people are trying to make Feralheart sound plural. And, quoting Devynex, it may be because of the deviantart group Feral-hearts. Another theory may be because people who call it Feralhearts might not be familiar with the game, is new, or does not speak English fluently.
Whatever the reason, Feralhearts is not the correct name for this forum or game.
Say?nara,
~ Rat Attack