Where is the human heart located in the chest?

Mandela Effect:

The heart is positioned fully left in the chest

New timeline: Slightly left in the chest

Many Effects concern themselves with the positions of the organs in the body. It seems they’re moving around.

Many think of the heart as “to the left”, but it’s only slightly so.  Do you remember things the doctor using a stethoscope on your left side? Now they place it right in the center of the chest. When shot, you clutch your left side right? The pledge of allegiance, hand over your heart, was to the left right?

So, where is it, and has it always been there?