This is such a cool concept for a card game! I feel like this has a lot of potential to expand on if you plan to make it a full fledge game! As for the scope of the Jam, I would suggest having some sfx or some ambience music to add to the experience of the game.
A couple of ideas from me is 1. maybe have a sort of 'rule book' to remind the game rule and object of the game that players can view at anytime, in case they miss something during the tutorial.
2. Since the game is about balancing the heart, I think having the heart counter be some sort of weighing scale would convey the game objective even better.
That being said, cool and unique game! Awesome work!