It may smell like rotten eggs, but it turns out H2S may be able to slow down the chain of chemical degradation that causes death in cells that are deprived of oxygen. Biologist Mark Roth can supposedly take a lab rat, stop its heart with a dose of hydrogen sulfide, and bring it back to life an hour later just by turning off the gas. Quoting now from this article at

Scientists are starting to understand that death isn’t caused by oxygen deprivation itself, but by a chain of damaging chemical reactions that are triggered by sharply dropping oxygen levels. The thing is, those reactions require the presence of some oxygen. Hydrogen sulfide takes the place of oxygen, preventing those reactions from taking place. No chain reaction, no cell death.

Roth has won a MacArthur grant for this work, so there’s a better-than-average chance that it’s more than just hype.