Very cool game. I enjoyed the difficulty personally. Just the right amount of heart-breaking. (don't take advice on difficulty from me though. You probably wanna make it easier when targeting a wide audience...)
Bonus points for making it possible to die on the win-screen. =P
Anyhow the gameplay is a really neat idea. As some people already mentioned it'd be great to also see some additional use for the heart, so it's not *just* a thing to get you killed. But jam-deadlines and all considered the given amount of mechanics is complex enough. Pretty sure there's a lot you could still explore without changing the mechanics much.
Oh. And please don't use 'space' for a non-jump mechanic in a game that has jumping. XD This killed me a good few times just because 'space' is usually the jump-key. Bind it to anything else. W, +, F11, just not space. =P