Project Summary Hypoplastic Left Syndrome (HLHS) has grown to be one of the most devastating congenital heart defects. Patients born with HLHS have an underdeveloped and dysfunctional left side of the heart and require a series of palliative interventions to correct the disorder and leave the patient utilizing their right ventricle (RV) as their main systemic pump. While palliation reduces the mortality of patients, it is still not a cure. Because of the systemic pressures and volume overload that the RV will now face over the patient’s lifetime, negative RV remodeling may occur and ultimately lead to heart failure. Negative RV remodeling can also present many of the same features that are seen in negative left ventricle (LV) remodeling, including hypertrophy and interstitial fibrosis. An injectable decellularized myocardial matrix hydrogel (MM) derived from porcine left ventricular myocardium has been shown to reverse negative LV remodeling and improved cardiac function in small and large animal myocardial infarction models. Additionally, it has been shown that the delivery of cardiac progenitor cells (CPCs) to the injured ventricle can enhance cardiac repair. The investigation of the individual and combinatorial properties of a RV based myocardial matrix hydrogel and CPCs as a potential therapy for right ventricular heart failure is warranted. The hypothesis is as follows: A MM hydrogel as a delivery platform for CPCs will lead to improved RV function via promoting healthy cardiac metabolism, reducing fibrosis in the infarct, and preventing cardiac hypertrophy in a rat pulmonary artery band (PAB) model for HLHS as opposed to either component alone. The hypothesis will be investigated via the following aims. Aim 1: To develop and characterize a RV derived MM hydrogel and assess the changes in survival, angiogenic and fibrosis gene expression and angiogenic paracrine signaling of MM encapsulated rat CPCs. Aim 2: To evaluate the efficacy of a combined therapy of MM hydrogel and rat CPCs and determine mechanism of action of a combined therapy of MM hydrogel and rat CPCs on relevant cell populations in a rat PAB model. The fabrication and characterization of an RV derived MM hydrogel and assessing its influence on CPC behavior will elucidate if the RV MM has therapeutic potential. Demonstrating the efficacy of the combinatorial MM/CPC therapy in a model of RVHF after HLHS palliation, will also justify further study into the therapy for usage to treat the failing RV because of other conditions, such as pulmonary arterial hypertension. Understanding the mechanism of action of the combinatorial therapy or either of its components alone on key cell types, will explicate important targets for the future of designing cardiovascular regenerative therapies.