The speaker talks to their own heart in blunt, unsentimental terms, calling it an "old whore." The insult is half affectionate, half disgusted: the heart is something that sells itself, wants more than it should, and "magnifies what it deserves," blowing up its own sense of what it is owed.
The second stanza lists what that deserving might look like: "a home and a road map / and another small heart." Settling down, freedom to wander, and a new love or perhaps a child are all wrapped together, and they pull in different directions. The word "small" makes the last item tender and a little fragile.
The ending drops into the language of a broken machine, "out of order," then shifts to the older, gentler phrase "much cast down." The speaker seems weary and rueful, laughing at the heart's greed while also admitting it is low. The mood is wry, tired, and quietly sad.