When Martina made the late Emperor's will public she faced staunch resistance to her playing any active role in government, but both Heraclonas and Constantine were proclaimed joint-emperors in February 641 without incident.

After Constantine died of tuberculosis in May 641, Heraclonas became sole emperor, under the regency of his mother due to his young age.

He reigned until October or November 641, when he was overthrown by Valentinus, a general and usurper of Armenian extract, who installed Constans II, the son of Constantine III.

[10] Under Heraclius, the Byzantine Empire was invaded in 639 by the Arabs, due to the failure of the Theme of Mesopotamia to pay tribute.

[13][14][10] A description of the ceremony is preserved in De Ceremoniis which says that the kamelaukion (caesar cap) of Heraclonas was removed from his head and replaced with the imperial crown.

[13][15] Heraclius died of edema on 11 February 641, leaving the Empire jointly to his eldest son, Constantine III, and Heraclonas,[16][12][17] who were both proclaimed emperor in late May 641.

[8][17] Shortly after Constantine took the throne, he was informed by his finance minister, Philagrius, that Heraclius had created a secret fund for Martina, administered by Patriarch Pyrrhus.

[19] Constantine appointed Valentinus as the commander of the main eastern army, in the hopes of retaining at least the Egyptian coastline.

[19] Heraclius' will also stated that Martina should serve as mother and empress-regent (sharing significant power), but this part was rejected by the Senate.

Because of Heraclonas' young age, Martina ruled through him, consistently opposing the policies of Constantine, leading to the creation of two different political factions.