If a real estate listing says a property is in the “heart” of a neighborhood, there’s a 50/50 chance that it's a) on the far edge of the neighborhood, b) a block or more beyond the far edge, or c) nowhere near the neighborhood in question.
Most of us think of the “heart” of a neighborhood as its geographic center. Real estate agents seem to think that a property that “hearts” a nearby neighborhood deserves to be described as at its heart.
YoChicago’s Neighborhoods page links you to authoritative descriptions of neighborhood boundaries. Bear in mind that neighborhood boundaries do evolve over time. You have to heart that.