After sustaining injury, cardiac tissue is replaced by scar tissue, which is less elastic and does not conduct signals as well. This results in decreased cardiac output due to poor contractility as well as secondary arrhythmias.
I was amused by my pawn's ability to fully recover his cardiac function after having his heart shredded by grenade shrapnel. In game, pawns already are unable to recover from brain damage, so I thought this suggestion might fit.
Just thought I'd put this out there!
so pacemaker implants ?
Maybe this was left out to decrease the number of involuntary organ donations from prisoners.
*puts on handwavey sci-fi author hat*
Obviously, in the future, humans carry a... genetic modification that allows them to completely regrow heart tissue. Oh, and bones. (Not eyes, though, judging by my colonists...)
I mean, it's 5500, they're bound to have made some improvements in the species. I'd hate to think we'd just been sitting on our laurels that whole time.