The main concept (2 worlds, switching between them) is interesting, although not fully explored. My favourite room was the one with 2 horizontal pits, and crystal obstacles; requiring the player to switch back and forth to advance. This highlighted a problem though; since the game requires switching back and forth between dimensions, there's no way to tell if you're a pixel out of range, before you switch.
This could be remedied by making the game grid-based, or by giving the player more landmarks to mentally chart where obstacles are.
The controls were quite awkwardly mapped, and more than once I found myself losing health due to grazing a pit edge.
With the fast acceleration of the character, it didn't feel too good to navigate. (Such as the blocks that the Player can move very quickly).
I was also unsure of how the "heart" theme tied into the mechanics.
Regardless, I think further exploring the "switching between dimensions" idea might prove fruitful, if you were to think of how it can engage the player more. This is the most interesting part of the game, and could be built upon. Good job on this.