This honestly reminded me of the old 8-bit cartridge game Balloon Man. Nice concept.
The gravity was a bit too strong though making it hard to shoot and float at the same time but maybe that's just me.
Just a few suggestions.
You can increase the number of small hearts that need to pass through for the health bar to completely go down and also reduce the speed at which the small hearts float up so player has more time to play and collect score.
You can also add floating power ups that restore a bit of the health, temporarily trigger auto shooting or auto floating for the player.
Overall it's a nice and challenging gameplay with cute art that matches the theme. It has potential so keep it up.