Build a super structure of 2x4s that will support the TV hanging hardwarezz and the weight of the TV. Make sure that whoever builds it puts in 2x8 or 2x10 blocking so that you can exactly center the TV over the fireplace opening without worrying about the chimney or where a stud is located. Have an electrician run the coax and enough outlets that allow you to plug everything in. Wrap the structure with fire-resistant materials or make sure that anything flammable is located a sufficient (per building code) distance from the fire box. Paint it up, then hang the TV and plug her in. There are hundreds of really attractive fireplaces with tvs hung above on houzz...

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Is It possible to lower the fireplace opening or the mantel?

Hi. Thank you very much for comments. I actually was thinking of complete redesign of this wall. I was thinking of removing mantel and installing the frame from floor to sealing around the fireplace and then installing limestone. Do you think it will look good in this room?

It sounds like it could be very attractive. This is what I did with my fireplace (before and after)