Got to level 15 and a lot of hearts, but then got 7 (!) minus hearts in a row, haha
Great game, the idea is very neat, even if it is simple and minimal. Bosses are cool, though I didn't feel much of a difference between lvl 2 and lvl 3 boss. Also the randomized levels which also progress in terms of their design was a cool touch, which made the game less repetitive. Great stuff overall!