That's a long time hypothesis of mine as well, but I think it stems from being stung or bitten by venom. If venom is injected into the bloodstream, it is desirable to be injected as far away from the heart as possible.

Some centimeters might not sound much, but over millions of years, the cumulative effect might be that 1% of human population every 10.000 years gets genetically optimized to hold their heart at a more protective spot.

Wikipedia on Situs Inversus (visceral organs are mirrored, heart on the right, liver on left) [0], mentions mixed results regarding handedness. There would be a load of other confounding factors here and I know nothing about medicine.

0 - https://en.wikipedia.org/wiki/Situs_inversus

If this was the case wouldn't it be easier to measure the pulse in peoples left wrists? Which doesn't seem to be a thing?

There is also a bias for how babies are held [1]. It holds even with left-handers. Holding a baby's head near the mother's heart helps the baby get to sleep. Which means the baby doesn't cry (and attract predators) and also gives the parents more time to sleep at night.

It also allows right-handed mothers to do something with their dominant hand while cradling the baby in that position.

[1]: https://sites.psu.edu/clarep/2024/04/12/the-left-cradling-bi...

Here’s my multiple years of anatomy classes response: the heart isn’t on the left. The aorta is, sure, but the vena cava is on the right. Also people with situs inversus (essentially all organs flipped laterally from “normal”) aren’t obviously more prone to left-handedness.

> Here's my five minute lunchtime hypothesis: it's because the heart is on the left.

Your hypothesis can't possibly be correct, because the only premise is false.

I wonder why you're getting downvoted? Even if it turns out you're completely wrong it's still an interesting point and something I never even considered before.