Although it's often listed as a horse harness buckle, this heart-embossed item is really a buckle shield, made to fit on top of the actual buckle. Supposedly, the shield would keep the buckle from snagging, but it also served an ornamental purpose. The same design has been around since the 19th century, and in fact it's still being made today.
It's also sometimes misidentified as a "Confederate blanket roll buckle," an unfortunate attribution which found its way into print into an early edition of Dr. Francis A. Lord's Civil War Collector's Encyclopedia, and into a later edition which reproduced the original pages without corrections. However, it was acknowledged in Vol. V, which was first published 'way back in 1989. Quoting from p. iv of Vol. V:
"Additions and Corrections to Volume IV, Civil War Collector's Encyclopedia.
"Page 27. Mr. Durham [Roger S. Durham, then curator of Fort Bliss Museum, Texas] identifies these blanket roll buckles as hardware from horse harness. He is very probably correct."
This mistaken ID was also debunked by Charles S. Harris, the author of Civil War Relics of the Western Campaigns, in an article titled "Hearts in Harness" in North South Trader's Civil War magazine, Vol. XXIV, #6 (Dec. 1997), p. 62-63, which was accompanied by several photographs showing identical buckle shields or covers in place on harness straps.
