Shape.MasterShape Property (Visio)
If this shape is part of a master instance, returns the shape in the master that this shape inherits from. Read-only.
Each shape in an instance of a master (the group and all its subshapes) points to its corresponding shape in the master. The MasterShape property returns the Shape object in the master from which the parent Shape object inherits.
If the parent Shape object is not part of a master instance, the MasterShape property returns Nothing.