Can an enlarged heart due to htn and/or mitral valve prolapse heal itself & return to normal size? If so, how? I have both mvp & htn.

Not likely. Once the heart is enlarged from a long standing problem, it will not go back to normal architecture though it may well continue to function normally if the enlargement is not significant. Sometimes, when the enlargement happens rapidly due to an acute issue, the size can go back to normal.
Not usually. MVP doesn't cause the heart to enlarge, but mitral regurgitation which accompanies MVP does and if it has, should be carefully evaluated for possible mitral valve repair with echocardiography. Be sure to keep your BP well controlled.