Abstract About one in four myocardial infarction (MI) patients progress to develop congestive heart failure, which has a 5-year mortality rate of 50%. The goal of this project is to understand post-MI roles of neutrophils by establishing how this cell type transitions in phenotype during wound healing spanning from inflammation to repair. We hypothesize that neutrophils undergo a temporal phenotype evolution that includes influencing post-MI inflammation resolution and ECM organization. Specific aim 1 will map neutrophil polarization phenotypes over the post-MI time course. Aim 2 will test the hypothesis that neutrophils actively contribute to inflammation resolution. Aim 3 will test the hypothesis that neutrophils actively contribute to extracellular matrix organization during scar formation. Innovation lies in the evaluation of neutrophil subtypes post-MI, which will allow us to connect early neutrophil cell physiology to late remodeling outcomes. Multi-discipline approaches will be integrated to explore the mechanisms whereby neutrophils regulate remodeling. This study will drive forward the understanding of the cellular basis of LV remodeling and identify novel intervention targets directed at neutrophils.