Previous parts here:

Creating a scientifically semi-valid super-soldier, part 1: Skeleton
Creating a scientifically semi-valid super-soldier, part 2: nervous system
Creating a scientifically semi-valid super-soldier, part 3: Physical shock resistance
Creating a scientifically semi-valid super-soldier, part 4: respiratory system

And one thread that has some information that is helpful: Is a double circulatory system useful?

In some sci-fi or fantasy, when they want you to know that some kind of creature means business they give them extra hearts. If you get an extra heart you have a spare one if the other one gets damaged, right? Often this goes along with some kind of super-coagulant that lets blood clot almost immediately, somehow without generating super-thromboses.

So the question is, how could you create an enhanced being that won't keel over if its heart is hit? This includes the circulatory system (might need a separate question later). The body should be able to build, maintain and repair this system.

I had two ideas on possible systems. The first is a lot like described in the "double circulatory system" thread linked above. Two hearts, each has a small circulatory system to one lung half (in case of an enhanced being with bird-lungs, two lung areas will be used). Then they pump it into the body. To preserve redundancy potential, the blood vessels each reach most of the body but each from the other end. So the right heart does the top of the arms for example before going to the bottom of the arms. If the right heart fails, the left heart will still supply enough blood to keep the top of the arms alive and slightly functional.

A big problem with such a system would be blood pressure. The blood vessels would need to be thinner because each heart pumps less blood per unit time and because they would take up too much space otherwise. This means that the blood quickly loses its velocity through your veins and needs to use your lymph system and muscle-pumps (normal contraction of the muscles pushes blood out and further).

Another option I thought off that could coincide with many systems, would be a peristalsis-capable blood system. This has two advantages. Even if the main heart stops the blood vessels would be able to pump the blood further, and in case of a blood vessel rupturing there is little need for high-strength coagulant if the blood vessel itself can squeeze shut and prevent further blood loss. The big drawback is, of course, the large amount of energy such a system would need.

So what would be good and solid options for a heart and circulatory system to work on an enhanced super-human or similar?

  • 1
    $\begingroup$ Are you allowing for cybernetic components or is this purely biological? $\endgroup$
    – Ummdustry
    Apr 13, 2018 at 21:54
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    $\begingroup$ @Ummdustry anything that the body could build, maintain and repair. $\endgroup$
    – Demigan
    Apr 13, 2018 at 22:06
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    $\begingroup$ Among modern combat injuries, blood loss is more common than a damaged heart, so consider ways to protect/duplicate/bypass key vessels, or musculature to essentially self-tourniquet. Chest injuries are likely to be complex - heart damage and collapsed lung and other damaged organs, so look at migrating some organs away and protecting others. $\endgroup$
    – user535733
    Apr 14, 2018 at 2:55
  • $\begingroup$ @user535733 I thought I had done that already with veins that can close themselves off when damaged? I would imagine that if someone was fast enough with closing it off that if someone cut them in half they would be able to survive (until they get finished off by whatever cut them in half that is). In that edgecase, the fact that you have two smaller Aorta's would be beneficial as they have a higher survival chance. $\endgroup$
    – Demigan
    Apr 14, 2018 at 21:35
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    $\begingroup$ I sort of covered it in the respiratory system question as it's linked, but similar to horses a backup supply of red blood cells in the spleen could help with blood loss. Beyond that, fast-acting clotting agents might be good (although you'd have to be careful about strokes and clots). Oh, and good old Klingon redundancy might not be a bad idea ;) $\endgroup$ Apr 14, 2018 at 23:44

3 Answers 3


So this is going to sound weird, but: separate the coagulants from the actual blood. Imagine a secondary set of veins wrapped around the actual blood vessels, containing a powerful coagulant. Whenever a blood vessel is opened, the secondary system is opened up too, and immediately begins reacting with the air. It quickly produces a plug over the injury, locking it down until the super-soldier can get back to base and get fixed by a doctor with access to a counteragent for the coagulant. Basically, it's an entirely organic bandage that applies itself. It plugs up any leaks quickly, without risking the blood itself sticking, and needing the coagulant to react with air (or maybe a special chemical seal the soldier can apply) prevents the secondary system from clogging.

However, this comes with risks of necrosis, since the plugs will block blood transfer. To this, I suggest one of two solutions. The first one is regeneration; give up saving the limb, and just let the soldier grow a new one afterwards. Hardly ideal, but the plug prevents exsanguination, and it's probably the easiest option if you can make super-soldiers anyway. The second is oxygen storage; put the injured limb into a kind of hibernation where oxygen needs are reduced. Likely it won't be able to do much, but neither will a lost limb, and the oxygen storage means that you're unlikely to lose the limb if it can be reattached afterwards.

A final note: I realize I haven't put any thought into protecting the heart with this. This is because I'm not sure HOW to protect the heart in a way that makes any sense at all. Anything that destroys the heart is probably going to also take out at least one lung and a few ribs to boot, and at that point it's just damage mitigation. A secondary heart would still have to contend with a gaping hole in your chest where the first one was, and a lack of oxygen from a missing lung. However, it could be wise to figure out a way to save the head, especially if regeneration is possible. Perhaps a secondary heart (yes, I know what I said) in the skull, capable of sealing itself and the veins in the head off from the main circulatory system, plus some lung tissue located in the mouth or trachea. Basically, a miniature circulatory system that exists solely to preserve the brain - if intelligence survives the rest may be able to be rebuilt, if your world allows it. (If it doesnt, disregard this.)

  • $\begingroup$ I think this is a very nice idea. On one hand having a seperate coagulant system all around your veins is going to take a lot more space, on the other hand if there's no coagulants being pushed through the veins there's more room for other stuff. Necrosis isn't that big of a problem similar to current coagulants. And don't forget that operations on the arm are usually done after preventing blood from being pumped in and they can last at least 7 hours without complications. As for the heart, I suspect that damage is most likely going to be from concussion forces rather than penetration. $\endgroup$
    – Demigan
    May 3, 2018 at 18:27

It could have like small heart-like structures spread all around in body, and system of valves making movement of muscles and even moving unconscious soldier boosting blood, so soldier could be revived (from unconsciousnes of cours) even by not-knowing-anything guy that stepped on body laying on ground for maybe up to week. So there wouldn't be any trouble, because it would be e. g. loops and loops going finger, lungs, finger, lungs, finger, lungs, finger, lungs, finger, lungs, finger, lungs, and get to looping from lungs to other organ. Also bloood would be thick, because red blood cells would be more densily packed into bloodstream, and veins would be like 1 mm wide, not like 0.1 mm like in normal person's blood stream.

  • $\begingroup$ Is 0.1mm the average diameter of all blood vessels, because if I remember correct, capillaries eventually get so small that they're only a single cell wide in the lungs. Even around other parts of the body, 1 mm seems a bit big; we have tons of blood vessels after all, and they need to be able to reach the cells of our other parts of the body evenly. Also why would the blood be thicker, and what parts of it? Platlets are what I seem to remember being the agent responsible for blood clotting, but too many of them causes thrombocytosis. $\endgroup$
    – Pleiades
    Apr 20, 2018 at 14:43
  • $\begingroup$ I'm unclear on your idea of the system of valves and its relationship to blood boosting abilities in relation to unconsciousness, and I also don't know why you mention the loops of going from I'm assuming a single finger back to the lungs because that's not how the circulatory system works, unless you meant something else. It's just a bit unclear at this point in time, but expanding these points could lead to a clearer and more useful answer to this question. $\endgroup$
    – Pleiades
    Apr 20, 2018 at 14:46
  • $\begingroup$ Do you perhaps have an idea of a non-heartshaped heart that could do this? It would be immensely energy consuming if you continuously have to suck in blood, basically stop it and then pump it further. I suppose some kind of peristaltic vein system might work in combination with the veins in the legs that use one-way valves to prevent blood falling back as it moves back up. $\endgroup$
    – Demigan
    May 3, 2018 at 18:31
  • $\begingroup$ I meant circulatory peristaltic system, valves making bleeding out almost impossibility and thickness would be caused by big number of erythrocytes and there would not be central point but web like medieval country; there is lot of cities and route using road A could be rerouted if road A would be destroyed. And moving uncounscious body is like carrying it around. $\endgroup$ May 7, 2018 at 12:54

A possible reason and concept for a dual circulatory system, is that one bullet or sword-stab (or shrapnel-stab or whatever) has a small wound channel and would therefore only damage a small-diameter cylinder. If you had two hearts, one in the usual place and one (say) pelvic, and each one was fed by one lung - add 'crossover' and shutoff valves - then a single rifle bullet would probably not damage both hearts. Priority in a human should go to feeding the brain and heart and lung and enough muscle to pump the lung; losing half its oxygenating capability would cripple the soldier but make it recoverable and fixable.

To prevent blood loss, expand the concept of arterial muscles to many MANY more and on the veins and lymph-system as well, so that 'damage' causes valves to shut. You'll eventually lose the area due to ischemia, but not the entire organism. Perhaps make it a reflexive but brain-controllable action, so that when the soldier or medic can examine the wound, the valves could be cautiously opened. (add a medical chemical to relax the valves for the same thing if the soldier is unconscious or too pained to re-open the valves)

Come to think of it, this might NOT be worth doing if the super-soldier is a mass-produced expendable. But I assumed we're starting with humans, which are expensive in terms of time (and calories of food) to produce (and grow to a workable size/state).


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