This engraving is based on an 18th-century painting of Alexander Nasmyth. It shows the location of the Heart of Mid-Lothian right beside St Giles' Cathedral. [Library reference Bdg.m.39].
The Heart of Mid-Lothian was a tolbooth, or jail, where people were held. The site was used for these purposes during the mediaeval period, but by the time that Scott came to write his novel it had become obsolete.
It was demolished in 1817, a year before the book was published. Scott himself obtained the iron-door entrance to the prison, which he later incorporated into his house at Abbotsford. Today a brick-mosaic in the shape of a heart marks the entrance to the Heart of Mid-Lothian in Parliament Square.