If i want the radiologist to compare orginal size of heart from 8 years ago in chest x-ray, do i need to go to the same radiology facility, where they have my prior chest x-ray?

See report: Either return to your first facility or obtain copies of the images and bring them to your new center.

See below: It is typically that the radiologist interpreting the most recent study make the comparison to the old study. I woud recommend getting a copy of the old chest xray and bring it to the recent radiologist for comparison.

No but need the X-ray: You should if the prior facility still has your X-ray. If so, they can "lend" it to you if on film or they can give you a digital copy on CD/DVD.