Six-Chambered Heart

I was thinking about a world/continent where reptiles are the dominant lifeforms and imagined that their three heart chambers divide into two, how would they compare to the four chambered hearts of archosaurs and mammals?

I don't think too many structural biologists hang out on these forums. Why, exactly, is this question relevant to your world-building? Are you trying to justify something with it or is it just a "cool fact" you thought up?

Reptiles are cold-blooded. That will make more of a difference to their physiological capabilities than the configuration of their hearts.

Edited by Fighteer on Jul 8th 2019 at 4:18:35 AM

Not exactly, monitors have what can be described as a 3 1/2 chambered heart and can grow very large and a very physical active. Plus the reason i'm asking is that the reptiles have a flexible honeycomb-like structure under their skin that stores heat and this heat is transported throughout the body via the circulatory system so they develop a more efficient heart to better accomplish this task.

The three chamber heart is less efficient than the 4 chamber heart since you get oxygenated and depleted blood mixing. However, structurally, the mammal heart and reptile heart are very similar with the mammal heart having a septum.

When you talk about a 6 chamber heart you're basically talking about a lizard with 2 separate hearts. Nothing wrong with that but I don't think it's what you're asking for.

Sounds like a metaphore for something...

Would that still accomplish the task of a more efficient circulatory system?

I don't see how it would but I don't know the exact setup.

On one hand, you can have all 4 atriums pump into both ventricles but this is really confusing and doesn't add anything but complexity. Maybe it's an attempt to divide and conquer a massive workload but it's still a net loss.

On another hand you can have 1 3 chambered heart for O2 rich and another for O2 poor but at that point there's no reason for 2 atriums per ventricle.

Finally, you can go with 2 separate 3 chamber hearts. What this lets you do is separate them and reduce the distance any given heart needs to pump blood.

Seems like a four-chambered heart would just be more practical then.

I suppose you could have two hearts in two separate locations, for a very large organism.

And then it would be a Time Lord.

Timelords have two hearts in the same location.

Because timelord.

I know this is only tangentially related but have you noticed that in many sci-fi stories when they have a creature/race with two hearts they have the ability to survive with just one? I think if a species had two functional hearts then the body would be designed in a way that both would be required for survival.

Humans have two lungs and two kidneys and in both cases it's possible to survive with just one. Losing a lung means you will have issues exercising strenuously, but will otherwise be fine.

Losing one kidney for the most part just means you can no longer lose a kidney and expect to be fine.

If a creature has two hearts and loses one, chances are it will be more or less analogous to losing a lung in humans. Strenuous exercise will be a problem, but for the most part the remaining heart will be able to pick up the slack.

Disclaimer: I am not a structural biologist.

Belisaurius's notes on potential configurations is missing a possibility: What if two atriums (A1 and A2) pump into two other atriums (B1 and B2) which then pump into two ventricles (C1 and C2)? That way you get a three step pumping where on the first beat the As are filling, the Bs are resting and the Cs are emptying; on the next beat the As are pumping into the Bs while the Cs are resting; and on the third beat the Bs are emptying into the Cs while the As are resting. With more opportunities for the muscle fibers to get little breaks, that would help with stamina, wouldn't it?

I figure that having six chambers might make sense if the animal is extremely large or can reach extreme heights (say through a long neck), as then you need extra pressure to pump blood through its body. It'd be especially important in the latter case, because you can't arbitrarily raise the body-wide blood pressure before blood vessels in the lower limbs begin to pop but having a separate circulation for the upper body parts would make evolutionary sense.