Whence the magical jewel came no one knows. Some say it is the veritable heart of a god, others that it is a star that fell from the skies long ago. The origins of this magical gem are unknown, although it was presumably fashioned using the power of the magical being Ahriman. It was held by Xaltotun in Acheron, 13000 BC, and was also known to another Priest of Set, Ptah Mekri, although it is not known if Mekri ever possessed the Heart. It was stolen from Xaltotun and he fled to Stygia, where his enemies later caught up with him and used the magic of the Heart to kill him. Three thousand years later, it was located by Orastes beneath the Temple of Mitra in the capital of Aquilonia, Tarantia. Orastes discovered its location "by devious means" after locating Xaltotun's remains in the subterranean temple of Stygia. Orastes used the Heart, and the power of the Old Ones, to resurrect Xaltotun. Xaltotun used his black magic to kill the king of Nemedia and all of his sons. Tarascus, as the younger brother of the king of Nemedia, then took the throne.
As Tarascus used his newly given powers to start an attack on Aquilonia, Xaltotun used his powers to paralyze Conan, king of Aquilonia and create an avalanche that killed many of the Aquilonia soldiers, including the captain that was masqurading as Conan because of Conan's inability to fight. However, Tarascus, fearing Xaltotun's power and not trusting his intent, stole the Heart of Ahriman from him while he slept. Tarascus gave the Heart to one of his soldiers, instructing him to cast it into the sea. The soldier, however, was slain by thieves, and the Heart stolen and sold to Zorathus, who took it towards Argos. Conan followed Zorathus and ended up finding him as a prisoner of Count Valbroso. Zorathus had been tortured to a point near death but had refused to tell them how to open the strongbox in which he kept it. When Conan promised Zorathus a quick death (as opposed to continued torture), Zorathus told Valbroso how to open the strongbox, knowing that he would be fatally poisoned in the process. Conan claimed the Heart, but, dumbstruck by its power, stared too long at it and was brained from behind by another, Beloso, who made off with the Heart.
Beloso escaped the pursuit of Conan, and he took the Heart to Messantia but was killed by a priest of Set who took the Heart to Khemi, in Stygia. Conan followed the priest to Stygia with the aid of black corsairs. The Stygian sorcerer Thutothemes obtained the Heart of Ahriman in Khemi from the men who brought it from Argos. Thutothemes sought to use the power of the Heart to revive the mummified Ptah Mekri, whom Thutothemes intended to train him in its use. However, Thutothemes was slain by four Khitain mystics, sent by Valerius to kill Conan, who hoped to take the magic item for themselves. Conan slew the last of mystics, the sole survivor of the battle against Thutothemes, but was then confronted by the partially revived, still mummified form of Ptah Mekri, who clutched the Heart. The semi-living from of Mekri proved susceptible to outside commands, which Conan correctly surmised. Conan forced Mekri to lead him out of the temple and then sent him back inside while he escaped. Conan gave the Heart of Ahriman to Hadrathus, a Priest of Asura, who used its power to counter the spells of Xaltotun, preventing him from interfering with the battle. Hadrathus confronted Xaltotun with the Heart, as Conan finished off the astounded wizard. From there, Hadrathus planned to replace the Heart in the cavern below the Temple of Mitra, "to burn as a symbol of the power of Aquilonia for a thousand years!"
The Endless Stair appeared, a manifestation that accompanied an event when Ahriman and Mitra would trade souls. An angel attempted to use this event to take a human lover in Red Sonja, but did not. Decades later, Conan retrieved the Heart of Ahriman to assist the druid Diviatrix against the combined power of Thoth-Amon and the Black Ring. The power of the Heart proved sufficient to overcome the entire coven of sorcerers, defeating and even destroying many of them. Thoth-Amon fled to the south.
In light of recent threats to Conan's kingdom, Hadrathus brought out the Heart of Ahriman, offering to use it to protect and defend Aquilonia. Conan turned down his offer. Crassus (a Set-worshipper posing as a Mitran priest) killed a Mitran priest named Dexitheus and blamed Hadrathus. Hadrathus stated that he was innocent of the crime to Queen Zenobia, and gave her the Heart of Ahriman as collateral if he was lying. Hadrathus was exonerated. Speaking with Trocero and Publius, Hadrathus (by this time a known confidant of King Conan of Aquilonia) showed them the Heart of Ahriman. He noted that it protected the kingdom from Crassus, a vile, Set allied adept. Trocero, Publius, and Hadrathus watched safely from a castle as a battle raged.
Later, Hadrathus used the Heart of Ahriman to divine the location of the Prince and Princess Radegund and Taurus. Hadrathus discovered that Crassus rode to Argos with Radegund as a hostage but had slain Taurus. Zelata, the blind prophetess, admonished Hadrathus, pointing out that the boy whom Crassus slew was a changeling of the real Taurus. Hadrathus used the Heart of Ahriman to observe Conn as the prince set out to slay Crassus. Hadrathus stowed away with the Heart of Ahriman as Conan set sail on a journey to confront Crassus. Hadrathus, once his presence on the ship was revealed, persuaded Conan that the Heart of Ahriman would be needed to defend themselves from Crassus. The Heart had the ability to greatly amplify existing magical powers.