Is the voltage at the heart the same as in limbs for ECGs?

When doing an ECG we measure the electrical voltage between two points on a person’s skin (for example for Lead II it’s right arm and left leg).

I am confused as to how the heart’s potential difference can travel all the way to the skin. It seems like the potential difference is not that big and I would be very surprised to see that small charge difference make it through blood which is constantly moving.

I would like a more physics heavy explanation if possible.