In the majority of human beings, the apex of the heart (left ventricle) points towards the left side of the body. Sometimes however (approx. 1/12000 births), a person is born with a condition known as "Dextrocardia", in which the apex of the heart points to the right side of the body instead.

Is there an evolutionary reason as to why the human heart usually points to the left side as opposed to the right side of the body?

(Note: Please don't answer with, "because there is a notch in the left lung", because I will simply reply with, "is there an evolutionary reason for the apex of the heart AND the cardiac notch being on the left as opposed to the right side of the body").

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    $\begingroup$ Also note there is a condition known as Situs Inversus with Dextrocardia, which is where the placement of all the organs in a person with this condition is a mirror of that of a normal person. $\endgroup$ – Kenshin Dec 27 '12 at 8:02
  • $\begingroup$ So I am asking that since people can live normal lives with Situs Inversus Dextrocardia, why is the placement of the heart on the left so much more common than placement of the heart on the right? What's the evolutionary advantage? Thanks $\endgroup$ – Kenshin Dec 27 '12 at 8:05
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    $\begingroup$ Is the orientation of the heart in humans different from other mammals? If not, then there would appear to be nothing special about humans. Heart orientation is just inherited from ancestral mammals. $\endgroup$ – kmm Dec 27 '12 at 19:07
  • $\begingroup$ Good point Kevin. I'm not sure if mammals hearts also are directed to the left or not. $\endgroup$ – Kenshin Dec 29 '12 at 16:37
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    $\begingroup$ sciencemag.org/content/306/5697/828.abstract seems to have the answers you seek. You'll need a subscription to Science though. $\endgroup$ – Chinmay Kanchi May 23 '13 at 17:42

From a quick look at the paper @ChinmayKanchi links to (Palmer, 2004) it seems that:

All living vertebrates possess a heart that is conspicuously asymmetrical and normally displaced toward the left (Fishman & Chien, 1997).

So the heart orientation seems to be evolutionary conserved in vertebrates (as are many fundamental traits), and no specific explanation is needed for humans.

This is said with the reservation that human anatomy is not my subject field, and the refered paper also digs deeper into the molecular basis for the orientation/symmetry of organisms. For instance, it also says that:

Second, the molecular pathway directing hearts leftward—the nodal cascade—varies considerably among vertebrates (homology of form does not require homology of development) and was possibly co-opted from a preexisting asymmetrical chordate organ system.

so the molecular mechanisms governing this seems to differ between species. This could indicate that there is a selective pressure molding species into the same heart orientation. This is pure speculation on my part though.

I also want to mention that evolutionary outcomes doesn't have to have a "reason" (i.e. a selective advantage). Much depends on chance events and evolution can only act on what is present at the moment (i.e. is restricted by earlier evolutionary history).


I think this deals with the steps of Heart development during organogenesis, together with the influence of external factors (such as the lung development and the hemodynamics), which by nature would lead heart to occupy the optimal positions for it and for those interrelated organs. Basically, the organs tend to develop on the midline, or symmetrically to the midline, but due to cardiac tube contortion during the development, it changes the position.

You can check the details on wiki (https://en.wikipedia.org/wiki/Heart_development)


I think it is because of the reason that the left ventricle pumps blood throughout body, thus is bigger than the right ventricle. So, actually, the human heart is along the center septum, but seems just a bit to the right. 1.5 cm to be precise.


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