Fragments Design Details: FrameShop Trace Editor

Click on the background. 

The Fragments field displays the number of fragments in the current design. A fragment is an object that is not enclosed, such as a series of lines, arcs, curves, or if the design has been exploded.

This two layered heart was exploded, so it now contains fragments. Once the fragments are reconnected, it would end up being two circuits; one for each layer.