There are perhaps a couple of underlying questions here. More specifically:
What is the system for regaining lost lives (hearts)? It seems you can buy them back (which I haven't tried) or collect a certain amount of band-aids (the number seems to increase each time you have to do it). I'm assuming the cost of a heart also increases, so my question is: how do each of these numbers increase?
What happens if you lose all your hearts? I'm not sure I want to find out what happens, although it seems there are a few achievements geared towards it.