What's your method for grinding for hearts? I do playthroughs of Chapter 11 (Viridi's first chapter). With a +3 Heart Bonus weapon modifier and level 4 Heart Booster power on 9.0 intensity, I can get over 130,000 hearts in one run. Here's a pic I snapped before meeting Cragalanche one time:
I find it to be relatively easy, especially if you pack in Instant Death Attack. That's the perfect power for beating green Jitterthugs, who require a high melee stat otherwise. The chapter also has a Rare Treasurefish in it, which gives over 37,000 hearts just on its own if you use the Heart Booster power in the conditions I mentioned above. There's also a Souflee that gives over 15,000 hearts. Have fun getting rich.
A lot of people like Chapter 20 (Palutena's Temple) for grinding, but I think that's better for loot than hearts.