Analysis of information sources in references of the Wikipedia article "Anastasia (wife of Constantine IV)" in English language version.
Heraclius' existence is only known from the fact that a letter was sent by Constantine to Pope Benedict II (684-85) together with locks of his children's hair. (Liber Pontificalis (Book of Pontiffs) 83: 'Like the clergy and army he [Benedict] received locks of the hair of the lord Justinian and of Heraclius, the clement emperor's sons, and also a mandate in which he intimated he had sent the hair'; Stratos 4.5-6.)