Injectable biomaterials are promising as new therapies to treat myocardial infarction (MI). One useful property of biomaterials is the ability to protect and sustain the release of therapeutic payloads. In order to create a platform for optimizing the release rate of cardioprotective molecules, we utilized the tunable degradation of acetalated dextran (AcDex). We created microparticles with three distinct degradation profiles and showed that the consequent protein release profiles could be modulated within the infarcted heart. This enabled us to determine how delivery rate impacted the efficacy of a model therapeutic, an engineered hepatocyte growth factor fragment (HGF-f). Our results showed that the cardioprotective efficacy of HGF-f was optimal when delivered over 3 days postintramyocardial injection, yielding the largest arterioles, fewest apoptotic cardiomyocytes bordering the infarct, and the smallest infarcts compared to that of empty particle treatment 4 weeks after injection. This work demonstrates the potential of using AcDex particles as a delivery platform to optimize the time frame for delivering therapeutic proteins to the heart.