Wherever the Upanishads speak of the heart as the locale for the ego, (Ch.U.VIII – 6 – 1, BrihadAranyaka U. IV-2-3) the Acharya speaks only of a ‘lump of flesh’ .
Even then it should not be taken to mean it is a full-fledged physical organ.
That is why the words “like the physical heart” were used above. It is the organ which pumps blood that is totally physical.
This heart however is in between the physical and the subtle.
The chakras that yogis speak of, and many of the nADis are totally subtle.
They do not fall in any X-Ray.
This heart also is not to be captured by X-Ray.