To use the heart seed you have to hold X when you pick it up.
Thank you very much for giving the game a try.
Viewing post in Unnatural: The Phantom Seeds comments
Ah, that did it! Thanks!!
One thing I might suggest after playing it a few times is that the game is pretty short. If you ever decide to update this it would be neat to be able to customize the amount of debt you start with. I got $10,000 in less than a week. I wonder how long it would take to get $100,000 or $500,000? You could even have an endless mode to see how much cash you could rack up before you die.