Recent controversies surrounding the authenticity of c-kit(+) cardiac progenitor cells significantly push back the advance in regenerative therapies for cardiovascular diseases. There is an urgent need for research in characterizing alternative types of cardiac progenitor cells. Towards this goal, in the present study, we determined the effect of maternal diabetes on Scal(+) cardiac progenitor cells. Maternal diabetes induced caspase 3-dependent apoptosis in Scal(+) cardiac progenitor cells derived from embryonic day 17.5 (E17.5). Similarly, high glucose in vitro but not the glucose osmotic control mannitol triggered Scal(+) cardiac progenitor cell apoptosis in a dose-and time-dependent manner. Both maternal diabetes and high glucose in vitro activated the pro-apoptotic transcription factor, Forkhead O 3a (FoxO3a) via dephosphorylation at threonine 32 (Thr-32) residue. foxo3a gene deletion abolished maternal diabetes induced Scal(+) cardiac progenitor cell apoptosis. The dominant negative FoxO3a mutant without the transactivation domain from the C terminus blocked high glucose-induced Scal(+) cardiac progenitor cell apoptosis, whereas the constitutively active FoxO3a mutant with the three phosphorylation sites, Thr-32, Ser-253, and Ser-315, being replaced by alanine residues mimicked the pro-apoptotic effect of high glucose. Thus, maternal diabetes and high glucose in vitro may limit the regenerative potential of Scal(+) cardiac progenitor cells by inducing apoptosis through FoxO3a activation. These findings will serve as the guide in optimizing the autologous therapy using Scal(+) cardiac progenitor cells in cardiac defect babies born exposed to maternal diabetes. (C) 2016 Published by Elsevier Inc.