Although those heelplates with a heart-shaped cutout (and other shapes of cutout) are in a relic-ID book as being civil war soldiers' heelplates, they've been solidly proven to be from Ladies' shoes. Notice that your heelplate is much smaller than a Men's-shoe heelplate. The intact Ladies' shoe in the photo below is actually a dug one, from deep in an 1880s town dump. Note the very narrow high "arch" of the leather sole, and small heel. I'm in the process of writing an article about them for the North/South Trader Civil War magazine, in my series of "Correcting The Record" articles on misidentified relics.