1. No magic
  2. Eat, drink, and breathe air (mammal/reptile(amphibian ok))
  3. Intelligent life form (no jellyfish or single-celled organisms)
  4. No artificial hearts (unless really ingenious, no swapping)

My thought:

A creature's veins/arteries were circuits and pulsed (kinda like esophagus bringing food to the stomach, except on a smaller scale). The veins would circle around the lungs and absorb oxygen and then distribute oxygen as it was pushed along. This idea is based loosely on the artificial heart that doesn't beat (summary=continuous-flow artificial heart).

Is it feasible for a foreign/alien creature to survive without a heart? Also are there any drawbacks to not having a biological heart or strange side effects?

To clarify, blood is not a necessary requirement if they can act intelligently. However, the creature must be organic/living: no AI robots. In my mind, a creature without a specific local organ to push blood/oxygen to its muscles would be harder to kill. It could still bleed to death as blood should be flowing in some manner to muscles, but there would be no particular spot to target to kill it instantly (excluding maybe the head, since there is no heart).

  • $\begingroup$ Just to be clear, the creature never had a heart or it was taken away? $\endgroup$
    – Vincent
    Commented Jul 23, 2015 at 18:35
  • $\begingroup$ It can be either or, but if it was taken away I don't want cases where it is replaced with just an artificial heart, since then it's still a heart. $\endgroup$
    – depperm
    Commented Jul 23, 2015 at 18:38
  • 4
    $\begingroup$ There is a huge difference between: how to survive without a heart and how to design a creature that does not have a heart at birth. $\endgroup$
    – Vincent
    Commented Jul 23, 2015 at 18:51
  • $\begingroup$ @Vincent I know there is a difference, from my idea of circuit veins and no heart from birth, is survival possible? $\endgroup$
    – depperm
    Commented Jul 23, 2015 at 18:54
  • 3
    $\begingroup$ There are a surprisingly large number of creative approaches to circulation in actual biology. However, it will be tricky to develop a system which does not create a specialized circulation device, but DOES create a specialized brain-like structure capable of intelligent, per the rules. Could you define the definition of heart you wish to use here? It'd be best if it was in terms of more generalized patterns (i.e. "the musculature which pushes the circulation forward is localized" as opposed to "a muscle in the chest"). The more general you get, the fewer loopholes we may find. $\endgroup$
    – Cort Ammon
    Commented Jul 23, 2015 at 19:16

7 Answers 7


Could one survive without a heart? Quite possibly. Assuming that is restricted to a single muscle whose job is to move a liquid around the body to move nutrients, gases and wastes.

Most animal-like things would need to have a delivery system to move things around. In replacement of a heart, all the bodies muscles could be used to move the 'blood'. All the veins/arteries could have frequent one-way valves. So the blood would have a round trip and as the animal moves it forces the blood to move. Not moving an arm, then the blood quits moving.

They would likely be more like reptiles in physiology, since metabolism changes a lot. The animal would also need to have some 'reactions' like breathing to keep a minimal amount of blood flow to vital areas. If these aren't 'cold-blooded' then they will need a LOT more food/body mass, since they won't have 1 organ tasked with circulation.

  • $\begingroup$ I simple and effective solution, instead of one massive pump, many small pumps instead. I'd just be curious whether it would cause enough blood pressure to fight gravity efectively. Though the creature doesn't need to be straight on two legs or be any humanoid shape at all, so it doesn't really matter. $\endgroup$
    – Necessity
    Commented Jul 23, 2015 at 20:14
  • $\begingroup$ @AdamNicholls many animals use leg muscles to help push blood back up... $\endgroup$
    – bowlturner
    Commented Jul 23, 2015 at 20:34

I don't think this is possible without a biochemistry very different than what we've seen on Earth. However, we don't know what life would look like if it was not carbon-based or oxygen breathing, so let's stick with those.

First of all, what does intelligence require? A lot of processing power. In humans, 15% of our blood flow goes to the brain. We need to be able to get this blood to the organism's CPU (the brain, in our case), and then back to the oxygen intake system (our lungs).

Here's where we start running into problems - the gas exchange needs to happen in an area with low blood pressure. The gas exchange can't happen if the walls of the blood vessel are too thick, so there's only so much pressure they can handle before a pulmonary edema would start to form. FYI, this is the case in fish as well, so being aquatic doesn't eliminate this problem.

What if the creature has a low blood pressure everywhere? It's not going to be able to pump blood everywhere in its system, especially not its energy-hungry CPU. Having arteries themselves pumping the blood isn't going to work - the blood looses oxygen along the way in order to power the artery-pumps.

One way to get around this is having a small size - with less distance to travel, the blood pressure doesn't need to be as high for the blood to get to all of the body. Unfortunately a smaller size limits the maximum size of the creature's brain, meaning that there would be a limit to how intelligent it could be. A size small enough to not need a heart would not have enough processing power to truly be intelligent.

So this naturally means that the creature needs to have areas of high blood pressure, and areas of low blood pressure. This requires some sort of pump to increase the blood pressure - a heart.

Are there any other ways around this? I can think of at least one - multiple air intakes. However, this comes with its own problems. The biggest one is disease. If you have multiple air intakes, that means you have more avenues for disease to attack and that your body has to keep defended. It would also be a vulnerability that other types of parasites could exploit.

So what about if disease and parasites didn't exist on a particular world? Evolutionary pressure must not be very high on a world like that, otherwise niches like that would be filled. Without evolutionary pressure, intelligent life wouldn't exist - intelligence is physiologically expensive, so it is only going to exist if there is some environmental pressure that it is able to relieve.

What about different biochemistries? As I said, we've never seen anything that's not oxygen breathing and carbon-based, so we don't know what it would look like. If you're going into the realm of non-carbon-based lifeforms, it would be reasonable to handwave away the need for a centralized heart.

  • $\begingroup$ When you say 'the blood loses oxygen along the way in order to power the artery-pumps' would this hold true if the veins used electric pulses to contract the muscles? I don't know exactly how or what goes into the creation of electric pulses $\endgroup$
    – depperm
    Commented Jul 23, 2015 at 19:47
  • $\begingroup$ @depperm that would require a new kind of muscle that doesn't use oxygen, a separate electrical pulse generation organ, and a change to the bloodstream to allow it to conduct current without electricity leaking significantly. FYI, electricity doesn't power muscles - it just signals to muscles that they should contract. $\endgroup$
    – Rob Watts
    Commented Jul 23, 2015 at 19:56
  • $\begingroup$ @RobWatts Is there any reason why the body would not balance itself, such that the arterial pumps do not consume all of the oxygen? Arguably its an efficiency thing. If you were 4x less efficient than a traditional heart, you'd only need 4x as much oxygen for these artery pumps as the heart used in the first place, and it doesn't seem all that inefficient $\endgroup$
    – Cort Ammon
    Commented Jul 27, 2015 at 5:17

In fact almost any muscle movement affects circulation somewhat. When you are walking or running, your legs aid your heart enormously by their pumping effect.

The skeletal-muscle pump is a collection of skeletal muscles that aid the heart in the circulation of blood. It is especially important in increasing venous return to the heart, but may also play a role in arterial blood flow. https://en.wikipedia.org/wiki/Skeletal-muscle_pump

enter image description here ... All you have to do is go into a suspended animation state instead of sleep (this would be like hibernation).

The rest of the time you would just have to keep on the move - the faster you run, the faster you can run.

I think this lifestyle would suit predators best. Lion-like (or cheetah-like) creatures could spend 95% of their day sleeping, then a quick warm-up before chasing the bejesus out of everything in sight. Fill your stomach and then straight back to sleep. The enzymes will continue to work even though you are not running around. Whilst resting, your stomach muscles could produce a slow, blood-pumping action whilst you digested your food.


Just to clarify before I continue this answer: I'm ignoring the mammal/reptile requirement in favour of the 'blood isn't necessary' requirement, as any creature that has no heart isn't going to easily fit into our normal tree of life. It might possibly be a shrub somewhere. Or a mushroom.

With that said: One potential (though unlikely) solution might be the generation of 'self aware' emergent intelligence in something like a man-o-war style colony. If this process proceeds long enough for all the creatures involved to be entirely co-dependant then it may be classified as one creature, despite being made from several.

This creature could be either ocean going or land-bound (my personal favourite environ for it would be a tidal estuary) and would be mostly sessile. It's also worth noting that the 'intelligence' would be distinctly different from ours, but no less valid.

In this creature there are many organisms, some of which prevent predation, some of which are responsible for luring/ensnaring prey, and some of which (the most interesting ones) exchange biochemical signals with each other and the other organisms in such a way that they can solve complex problems/ be aware that they are a thing. Imagine an ant colony, but with the ants being microscopic, numbering in the billions and having had some serious pressure to evolve more complex problem solving mechanisms.

This organisation would have a distinctly different structure to a human brain, potentially manifesting as a constantly shifting sense of self, no discernible personality, or very short term memory when not actively working to resolve a problem. It's possible that this creature would have no interest in putting a jigsaw puzzle together if you asked it to, but would solve a 12x12 Rubik's cube to get some food from the middle of it. It would also have some serious processing lag. While it might be able to reconfigure to solve hideously complex problems, the signal delay between individual cells not bound into a structure like our brains are would approach situations in a dreamlike fashion. Don't expect fast reflexes.

This creature would have no 'heart', no 'brain' and no 'hands'. Some organisms might be responsible for nutrient transfer, but if it's similar to a man-o-war there would be no distinct resource transfer network, just an organisation of specialised cells that can be re-organised by the emergent intelligence as best required. Some organisms work together to solve problems and keep every other organism (and themselves) alive, but loss of a section of them will be patched up by the others (though it might cause confusion). Some organisms might be great at organising into temporarily strong structures for object manipulation, but without guidance from the 'brain' cells they'd just form a lichen-like blob.

It would be extremely weird to watch this beast doing anything. Imagine this thing trying to use a can opener on a tin of spaghetti. It would pull the can and the opener into itself, take a few seconds experimenting, then open the can inside itself before drawing the spaghetti and sauce out into a slowly diffusing mass of nutrients. Movement would be less of an active 'I am going here now' and more of a gradual relocation, like watching a banana tree move, or tracking a city over the course of millennia.

TL:DR: Beached man-o war/Uber-ant colony. No heart as it's distributed, intelligent because it's got complex emergent behaviour, and can eat/drink/breath/manipulate, just really weirdly.


Suppose you drank with your feet, and steamed off with your head. Interstitial fluid is then being drawn upwards by osmosis or vacuum forces as the water evaporates. This continuous flow of water carries nutrients through-out the entire body. If you want to use your arms, then you would also need to take a drink with your hands. You wouldn't need veins as such, just a network of capillaries.


Peristaltic blood vessels.

Increase slightly the outer diameter of the tunica of all major blood vessels, and have them pulse according to an internal pressure-controlled feedback loop. Human beings have already all the required organs and subsystems, so we know that it is possible.

All arteries are surrounded by a smooth muscle layer, that contracts and releases once per second (this might be too much for smooth muscle, and we might require striated or cardiac muscle fibers), and generate a pressure wave traveling at about 1 meter per second. You have now a heartless circulating system with no single point of failure, as far as pumping is concerned. The muscle work to contract about 5 millimeters against a pressure of 150 mmHg (0.2 kg per cm2) over a surface of around (my estimate) 2400 cm2 is 0.005*0.2*2400 = 2.4 N, so we're talking of less than 3 W (which is consistent with the fact that a low-efficiency thermodynamic capacitor for an artificial heart was estimated to require 16W of thermal power).

So, the energy and oxygen requirements of the "distributed heart" are negligible and can be easily satisfied by the existing supply methods.


Bugs, insects, and many invertebrates do not have hearts, not even a complete circulatory system. Instead, they diffuse oxygen throughout their bodies via microtracheae, which pulsate to make their bodies a little like a giant lung. This is why you can not drown an ant or a cockroach by submerging their heads.

Bugs sometimes have a heart for pumping hemolymph, or basically highly concentrated fuel rich bug-blood that works mostly via diffusion. Worms and a lot of smaller bugs do not have any form of significant heartbeat (though many have a primitive heart-like organ to stir the hemolymph around) or any significant blood pressure (as the blood does not carry oxygen).

You can easily scale up such a system by having baffles around the trachea that constantly stir or move the hemolymph, or having other organs (or constant bodily motion of the body walls) that pump this liquid around. Bugs actually do get large in some places. For intelligence, just make your atmosphere oxygen-rich or increase the pace of the pulsating trachea, and having multiple nerve ganglia instead of a single solid brain.

There are already working examples of such life being perfectly immune even with this multi-intake scheme. There are insects, after all. Because of this form of respiration, bugs are actually defined as bloodless by certain Semitic traditions.


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