Thats a fun little game :) But what if the heart is healed from love? Will it become cold and unable to ever love again? o.O You could add a little trail effect to the Heart and to the enemies to make the scene a bit more alive. And a death animation. I am thinking about blood effects like in the classic doom game, but thats might be too over the top :D I think the speed difference between enemies and player is ok now. The hitboxes are very accurate. If you made it a bit smaller than the actual sprite, the player would have more "oh gosh, just barely made it through"-moments.
Thank you for your comment :D Trail would be nice but I think, that if I add it to everything that moves it'll be too much effects on screen :P I thought about this game as a little post-apo game :P Death animation is great idea thou :D I'll think about adding it later :D
EDIT: I checked how will it look with trails and in a few minutes I'll upload that version, thanks again :D