ELI5: Why do people die instantly when a bullet passes through their heart?

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Your blood pressure essentially drops to zero and you black out. Technically there is still some brain activity going on at this point, but considering you will be unable to maintain consciousness and you will die shortly after, its fair to say its instant death.


a direct hit will cause near-instant unonsciousness. This has nothing to do with breathing or blood oxygentation, its the sudden drop in blood pressure to the brain because the heart no longer pumps. The brain needs contant blood flow. This is also why chest compressions are more critical can than breaths in CPR.


People **don’t** die instantly when shot through the heart. A “worst case” scenario is a complete loss of blood pressure. Which means that you become unconscious within 3-10 seconds. If the bullet doesn’t shred the heart or the aorta (and instead nicks a heart artery) the effect isn’t nearly as fast and it will take several minutes (or even several hours). Then it takes another 5-ish minutes for the cells most vulnerable to oxygen deprivation to die (your braincells. Other organs, such as muscles, can survive far longer). This is because there is a pretty big difference between the level of energy needed for cells to perform work (like thinking) versus just maintaining cell function. If bloodpressure with oxygen rich blood is restored within that limit there is a chance to revive the victim (not likely if the aorta or heartchambers have been shredded). P.S: The only case where people “die instantly” is when there is extensive damage to the brain or brainstem. The cells (well, the ones that haven’t been ripped apart) will live on for a few more minutes, but the ability to maintain “you” is gone pretty much instantly.


Another thing to consider is what part of its cycle the heart is in when a bullet slams into it. If it’s gets hit the moment it’s pumping then it can cause a massive spike in blood pressure throughout the body which bursts blood vessels in important places, like the brain, and causes immediate brain trauma. (Read this in a hunting magazine years ago when they figured out why big game sometimes dropped suddenly when shot through the heart, and sometimes didn’t. I’m assuming the same thing could happen in humans.)


What exactly happens when your heart gets punctured by a bullet: 1.) When the heart gets punctured by the bullet, the blood starts flowing out into the mediastinum (the space in thorax where the heart and lungs are). This blood soaks the lungs and the lungs collapse, making breathing far more difficult. Think of it as a big hemorrhage in your thorax, where the thorax gets filled with blood from within. 2.) Because of the hole made in the heart by the bullet, the blood instead of circulating normally through its physiologic pathway, gets diverted. This leads to a sudden drop in blood pressure. This drop is blood pressure is low enough to trigger a syncope (loss of consciousness) which eventually leads to death in a matter of a few seconds. 3.) Because the BP has dropped, the blood isn’t really moving much. This triggers the coagulation which leads to the formation of thrombi (blood clots) within several vessels which further accelerate the processes such as, getting a stroke and organ failure. To sum it up, it might take a few seconds to a few minutes for the person to die. This entirely depends on how big the wound/damage is. If the bullet used is really small and is travelling at a relatively slower velocity (bb gun fired from a distance), it will nick the heart but won’t cause as much damage as an AK would, when fired from the same range.