A special kind of scarab, known as a heart scarab, was placed in the wrappings of Egyptian mummies approximately over the heart. It was larger than the scarabs worn as seals or as amulets by living people, and it was generally made of stone, as decreed by the Book of the Dead, which also ordained that it should be put in a gold setting. Tutankhamun's heart scarab, which was suspended from his neck on a strap of gold wire, was placed near the navel. It was made of black resin mounted on an inscribed gold plate with a cylindrical eyelet at the head end for the suspension strap. A figure of a heron (Ardea cinerea or Ardea purpurea) in polychrome glass was inlaid on the back of the beetle.

As a rule, the main purpose of a heart scarab was to prevent the heart, which the ancient Egyptians regarded as the seat of intelligence, from giving evidence against the deceased owner in his judgment before Osiris. It was generally inscribed with a spell from the Book of the Dead (Chapter 30 B) and it was from the words in the spell that part of its magical power was thought to be derived. Tutankhamun's scarab bore a different inscription, which will be described, and in that respect it was not typical. But a heart scarab was not intended solely for use on Judgment Day. It was the symbol of the creative power of the sun-god and, through that power, it was supposed to restore life to the heart of the dead person. Furthermore, in the hieroglyphic script, the word meaning "transformation, metamorphosis" was written with the scarab sign, and the heart scarab was believed to provide the deceased with the means to transform himself into one of the various living creatures, which included the heron, enumerated in the transformation spells of the Book of the Dead (Chapters 76-88). Tutankhamun's heart scarab, with its inlaid figure of a heron, was evidently designed to fulfill that function, in particular, through the normal processes of imitative magic. No copy of the Book of the Dead was placed in Tutankhamun's tomb, although some excerpts from it were inscribed on the walls of the gilded shrines that protected his body.

The heron or, to give it its Egyptian name, the benu bird, was deified in very early times, probably because of its habit of wading in shallow waters when the Nile was receding after the annual inundation. It was the first living creature to stand on the muddy soil each year, surrounded by water before the flood had completely subsided. In such a setting it reminded the early Egyptians of the initial stage in the Creation, when life first emerged from the waters of chaos, and it supplied them with a concrete image that symbolized the first act of creation. The benu, in consequence, acquired the epithet "He who comes to life through himself," or the self-generating. Tutankhamun, through his heart scarab, not only possessed the ability to transform himself into a benu, but was also able to regenerate himself at will.

In historical times the center of the benu cult was at Heliopolis, which was also the center of the more powerful sun cult of Ra, whose priesthood could not recognize the existence of any deity earlier than their own. The difficulty was overcome by postulating that the benu was simply a form assumed by Atum or Ra from the time of the Creation onwards, and a similar explanation was later adopted by the adherents of the Osirian cult. It was this external manifestation that was called by the Egyptians the ba. Tutankhamun, by the very fact that he had been transformed into a benu, became the ba of the sun-god, and of Osiris, too, and it is in that capacity that he represents himself in the inscription engraved on the gold plate beneath the scarab. It reads: "Words spoken by the Osiris, king Nebkheperura, true of voice, 'I am the benu, the ba of Ra, who leads the blessed dead to the Underworld, who causes their bas to go forth on earth to do whatever their kas wish.' [So saith] the Osiris, the Son of Ra of his own body, Tutankhamun, Ruler of Heliopolis of Upper Egypt, true of voice." The ka has been defined as a person's "self", his individuality, but it is, like ba, a word that has many different shades of meaning.

The value of the heart scarab lay not in its material or in its artistic qualities, though the heron is exquisite, but in its magical properties. For Tutankhamun it was perhaps the most important of all his amulets.