This question goes back to my Ender's Story, so eventually somewhere in the plot a woman is going to be stabbed directly in the heart, but she has regenerative abilities, I would like her to die, but I want to know the scale of the fastest regenerating powers could be without being able to survive a stab to the heart. Imagine that the regenerating abilities are cause by an endorphin generated by the brain which sends it to the heart and adds a specific type of blood to the blood stream that clots wounds faster (stops the bleeding) ad repairs it self. (like for example if her arm was chopped off how quickly could it regenerate under ^^^ these circumstances)
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A stab wound to the heart is going to result in three very major issues right away:
- Trauma: While there are supposedly recorded cases of survivors, puncture wounds to the heart have an almost universally grim prognosis. Firstly, the wound required to puncture a heart will also have to pass through the chest, damaging other tissues, bones, and organs along the way. On top of that, the heart itself is quite sensitive to damage, and will begin pumping irregularly or stop pumping altogether if it is damaged. Even blunt trauma to the chest is a concern for this reason, wherein the heart is usually only bruised, or ruptured in the most serious cases.
- Blood Loss: Opening a wound directly into the heart will rupture any number of very significant blood vessels which will bleed internally and externally. Blood is required to oxygenate the brain and the rest of the body, so even if the heart does manage to survive this injury the body will still be lacking a critical volume of blood.
- Shock: Circulatory Shock occurs when not enough blood is reaching bodily tissues. Blood loss is an obvious cause, as is cardiac arrest. The inflammatory response of most tissues in the body causes further circulation problems leading to significant cell death.
Despite the severity of the injury, the real organ we need to be concerned with is the Brain. Most bodily tissues can survive prolonged nutrient deficiency (with permanent damage, perhaps) but the brain is more sensitive. The agreed upper limit on brain survival without oxygen seems to be about 4 minutes, though this is usually in a controlled medical environment; brain damage is still possible in far less time.
Regenerative powers will have to address the major issues right away, and in enough time to mitigate the oxygen deprivation they cause.
- Firstly, the heart and its surrounding cavity will need to be healed. This is a slow process in real life, sometimes taking months even for minor injuries. To heal completely in under four minutes your character will need ridiculously fast healing, something like 43,000x faster than normal.
- Secondly, she will need to deal with the blood loss. Loss of volume under 30% is usually recoverable without transfusion, but anything more will require immediate production of more blood, which will be difficult since blood production requires lots of water and nutrients.
- As long as the first two issues are covered, the Circulatory Shock should be mitigated. Adrenaline might help, but its use is usually for anaphylactic shock, not circulatory.
So, if you're looking for some reason your character should not survive, then any of the above requirements make a perfect candidate for removal. You might also note that if the catalyst for this rapid healing/regeneration is some sort of chemical/hormone, then damage to the heart will prevent its circulation, thus limiting its ability to function.
Disclaimer: I am not a doctor, so keep that in mind.
The way an injury to the heart kills is by stopping the heart from beating efficiently, or causing the heart to leak which either causes exsanguination, or pools around the heart and makes it so that the heart can't pump. The net effect of either of these is that oxygenated blood isn't being pumped to the brain, causing the brain to die.
If the heart stops beating completely then the endorphin won't be able to circulate to the heart to trigger the healing.
If the heart is leaking blood then at least the process can be started.
In either case though, where at some point the blood isn't flowing, or there isn't enough of it left in her, the brain will still need oxygen, and that's your time limiter.
In the case of animals professionally exsanguinated for slaughter, brain death can occur in 10 seconds. A heart injury would not be that fast though, as residual oxygen in the blood would probably keep it going for a minute or two, especially if the heart stopped beating and stopped draining the blood from her body.
In theory, if there was a way to keep the brain oxygenated, or if the regeneration ability was fixing the tissue as fast as it can fail, then she could be "dead" for a while without negative effect. How long depends on how efficient the process is.
If a source of her regenerating powers is faster-clotting blood, she'll get a thrombus near the heart, causing some form of myocardial infarction and possibly - if she was stabbed in the
right wrong place - completely stopping blood flow to a heart. So, the faster she regenerates, the less likely she is to survive.