NAD.

Having said that, if your “primary” heart is having issues it’s usually something that a second heart wouldn’t be able to bypass.

For example, if the heart chambers are just fluttering then your second heart could try to take over, but I imagine that if the primary failing one would cause so much ruckus that the secondary wouldn’t be able to keep up normal blood flow.

I imagine a better system with some electronics that can either work as a pacemaker or take over completely in an emergency situation by just plain stopping the heart and taking over until help arrives, or something like that.

Again, NAD