Constantine III (3 May 612 – 20 April or 24/26 May 641) is Byzantine Emperor for four months in 641.

He is the eldest son of the Byzantine Emperor Heraclius and his first wife Eudokia.

Constantine's birth name was Heraclius Novus Constantinus, which is also the official name under which he reigns.

The name Constantine became established in later Byzantine texts as short for the Emperor and has become standard in modern historiography.

In terms of official Imperial nomenclature, the style "Constantine III" would be more appropriate for his son Constans II (r. 641–668).