The idea behind the game is really creative and peculiar. The waves system and upgrades make the game progress cool to experience. I'd like to see a full version of this game, it would be a great indie game. Also I'd like suggest an improviment: When the heart shrinks, the animation stays the same as when it expands. If it was just a little bit different, it would be easier to attack in the right time.
It's a good game with a lot of potencial. Congrats to the developer!