Injectable scaffolds made of biodegradable biomaterials can stabilize a myocardial infarct and promote cardiac repair. Here, we describe an injectable, citrate-containing polyester hydrogel which can release citrate as a cell regulator via hydrogel degradation and simultaneously show sustained release of an encapsulated myeloid-derived growth factor (Mydgf). Xu et al. described the synthesis of hydrogel with biocompatible starting chemicals including citric acid and poly(ethylene glycol) diol. The characterization of materials demonstrated that the developed hydrogels possess tunable degradation and mechanical properties and exhibit sustained drug release. The authors also observed improved postmyocardial infarction (MI) heart repair in a rat MI model through coupling the therapeutic effect of the hydrogel degradation product (citrate) with encapsulated Mydgf. In their study, hematoxylin and eosin (H&E) staining and Masson’s trichrome staining were performed on heart samples to evaluate the change in heart structure. Furthermore, immunohistochemistry was used to study neovascularization. Their results showed that the intramyocardial injection of Mydgf-loaded citrate-containing hydrogel significantly reduced scar formation and infarct size, increased wall thickness and neovascularization, and improved heart function.