Celtic knot charm, 1" x 1/2". This pattern is often call "Trinity and Heart", as it combines both symbols. The charm has a rough hewn finish on the top. - it is not mirror smooth, but is meant to look carved. There is a tiny defect in the casting, upper left - this adds to the carved look, although I think it was unintentional. The reverse is marked 925 and Sterling.
The former owner must have worn this as a pendant. I can change this to a traditional sterling jump ring at your request. (No charge.)