The heart in the Basilica taken by Pelletan has a totally undisputed history from 1830 onwards although there is still documentary evidence for it being in Pelletan's possession before that. The 1998 DNA tests proved that it was the heart of a male child between 7-10 years of age and that this child was unequivocally the son or possibly the grandson of one of Empress Maria Theresa of Austria's daughters.
Of these, only four of those that made it to adulthood had issue. Maria Christina of Teschen, who had a daughter that died in infancy (a day after birth), Maria Amalia of Parma who had 9 children only 3 of which were boys, her eldest lived to adulthood, and the younger two died at a few days and 3 years respectively. Maria Carolina of Sicily had two sons who survived into adulthood and of the male grandchildren through Maria Amalia and Maria Carolina's daughters there are no princes whose hearts would accurately match or have been available to Pelletan.
That leaves Marie Antoinette who had two sons, Louis Joseph and Louis Charles. Given that the heart was known to be in the hands of Pellatan who is proven to have also examined a deceased male child in the Temple in 1795, and the complete lack of male candidates available from Marie Antoinette's sisters, ( the two aunts DNA that was tested, Maria Johanna and Maria Josepha died without issue) then the heart HAS to belong to either of Marie Antoinette's sons with all the supporting evidence pointing to Louis Charles.
Louis Joseph died aged 7 and was buried in the Royal tombs at St Denis. These were destroyed during the revolution in 1793 and the bodies removed and despoiled. However, the burial custom for the princes/Kings of France was for the heart to be removed at death and then embalmed ( this is what prompted Pelletan to remove the heart in the first place) The heart of Louis Joseph was removed and embalmed ( records prove this) not stored in alchohol as was the heart kept by Pelletan.
Therefore the heart tested in 1998 can only be that of Louis XVII, there are no other viable candidates that the heart could belong to.