The material was discovered in Romania by Franz Nopcsa, in the late Maastrichtian Sânpetru Formation (Rognacian faunal stage, deposited c. 68 - 66 million years ago) of the Haţeg Basin in Transylvania. The scientific name means "C.W. Andrews' Transylvanian bird", after the namer of Elopteryx, and Ancient Greek (h)epta (επτά) "seven" + asty (άστυ) "city" + ornis (όρνις) "bird"; the Latin septum urbium or the German Siebenbürgen - meaning "seven cities" or "seven castles" - were common names for the Transylvanian region throughout the centuries.
The material was originally limited to a mere two broken distal tibiotarsi, BMNH A4359 and A1528. The taxonomic status and systematic placement of these bones was much disputed and they were often considered junior synonyms of Bradycneme or Elopteryx. Given the fragmentary nature of the fossils, little could be resolved and Heptasteornis was (and still is) considered a nomen dubium by many.
However, more recently the bones were reassessed as an alvarezsaurid, the first to be known from Europe, and this theory, originally proposed in 1988, has since withstood further scrutiny. Bradycneme and Elopteryx on the other hand seem to be more advanced maniraptoran theropods.
Thus, quite ironically, of those three enigmatic Romanian theropods the one most explicitly named a "bird" - as per its scientific name - is almost certainly the one most distantly related to birds.