Hi SAS1.
I am not a doctor; nor a nurse; but, I believe the chances of your heart returning to its normal size and you being able to resume good health if you continue to walk and loose weight is super!
I have faith that this is extremely possible and that it can and will happen for you! : )
Have a Blessed day in the Lord. Be peaceful and happy.
Take your medications, I believe high BP can contribute to enlargement of the heart, I know too much pressure in the atrial chambers, e.g., leaky valve to ventricle (power pumping) can cause enlargement.
To your question, I have an enlarged left atrial chamber and I am several years older than you. The surgeon who repaired my mitral valve said my enlarged atrial chamber could shrink back some now that the "back pressure" is gone. He did not expect it to return to normal size.
I think the key is to stop the enlargement process. That accomplished I believe continued good heath practices, including getting weight down to recommended level, will make you feel and look a lot better, and that will make help mental attitude which is also a big plus.