Totally agree on the lack of checkpoints being a little too brutal as someone else has pointed out (weird oversight on my end). Will possibly fix that!
However, I don't know if I agree with the dropping of hearts. I feel adding checkpoints would solve the same problem (quick restarts would mean failure wouldn't feel so bad); due to enemy respawns, I feel heart drops would be a little easy to grind; and part of the intended challenge of the game is managing your health and choosing when to take the health downgrades.