The heart scarab was an amulet placed on the chest of the mummy to ensure that the heart, believed to be the seat of intelligence and personality, was not removed. A verse of Spell 30B of the Book of the Dead is roughly incised around the base of the scarab. The appearance of Sobekemsaf's scarab follows the instructions of the spell exactly, being 'made from green stone, mounted in fine gold'.
Spell 30B was apparently very old, perhaps composed during the Old Kingdom (about 2613 - 2160 BC). A heart scarab of the Thirteenth Dynasty (about 1795 - 1650 BC) suggests that they were first produced in the Middle Kingdom, around 400 years after the spell was supposedly composed. It seems that a false pedigree was created for the spell, so that it appeared older than it was. This illusion of antiquity is also used to validify the 'Memphite theology' on the Shabako stone.
C.A.R. Andrews, Egyptian mummies (London, The British Museum Press, 1984)
I. Shaw and P. Nicholson (eds.), British Museum dictionary of A (London, The British Museum Press, 1995)
J. Capart, A.H. Gardiner and B. van de Walle, 'New light on the Ramesside tomb-robberies', Journal of Egyptian Archaeol-8, 22 (1936), pp. 169-93.