Heraclius, with Heraclius Constantine. 610-641. AV Solidus (20mm, 4.44 g, 7h). Constantinople mint, 7th officina. Struck circa 616-625. Crowned and draped facing busts of Heraclius and Heraclius Constantine; cross above / Cross potent set on three steps; Z//CONOB. DOC 13f; MIB 11; SB 738. Choice EF.
Although the officina letter resembles a vertical K, this would not fit in the series. A poorly formed Z is a more logical interpretation.