Can I die if I still have soul hearts?

Question

Can I die if I have soul hearts but lose all my red hearts, either from making a deal with the devil or using the razor or using the blood donation machine?

Answer

This answer is a little tricky.

You are not supposed to die. Soul hearts function just like regular hearts for the purpose of keeping you alive. So in most cases, as long as you have soul hearts, you won't die.

Making a deal with the devil, however, is slightly different than the other examples you've given here. While using a blood donation machine or the razor will cause you damage, making a deal with the devil will actually make you lose regular heart containers. This is probably the reason that making a deal with the devil can get you killed even if you have soul hearts left after the deal, though this is actually a bug:

Bugs:

• If you have hearts and soul hearts and make a purchase that uses all of your regular hearts you will also lose all of your soul hearts. You will then have no hearts shown in the top right but still be alive.
• If you have hearts and soul hearts and make a purchase that uses all of your regular hearts you can be killed despite still having soul hearts.
• If you have a 1-Up and you make a deal that kills you, you will come back with no heart capacities, and will still be alive, and you will be unable to gain more heart capacities.

(Taken from here)

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