Of All Things - Shakespeare's Monkeys

Your form is prose, yet this could easily be poetry by adding line breaks and tightening the language. Examples of how you might do this (/=line break):

"Some days I cannot breathe / cannot breathe without a pain / a lump, a knot inside my lungs / beneath my ribs / near to my heart. / A hole in my chest / in place of a heart..."

Of course, it's OK as prose, but I really think it would make better poetry. In either form, you have a lot of redundant and unnecessary words. Example: "but it lives there no more". By saying "should reside", you've already indicated it isn't there. If you wanted to express that it was once there but is no longer so, the previous phrase could be"where my heart once was", which implies clearly that it is no longer there.

I do like the feelings and ideas expressed here, but I think you could tighten up the writing to make it more effective. As for changing it to poetry, this is perhaps an expression of my own bias as a poet, but in any case, this piece would adapt quite nicely.

Alcuin