Abstract Heart failure (HF) is a leading cause of morbidity, mortality, and escalating health care costs within the VA. The type of HF that is increasing disproportionately is HF with a preserved ejection fraction (HFpEF), commonly caused by left ventricular (LV) pressure overload (LVPO). A cornerstone of HFpEF is LV diastolic dysfunction and extracellular matrix (ECM) remodeling, in which these structural changes are not readily reversible. A critical pathway for ECM remodeling is post-transcriptional regulation by the microRNAs (miRs). The guiding hypothesis of this collaborative program is that a specific and quantifiable shift in a specific miR profile, which regulate key ECM processes and can be identified in both HFpEF patients and a large animal model of HFpEF, is predictive for exercise response and attenuation of HFpEF progression and mechanistically directs phenotype reprogramming of HFpEF myocardial fibroblasts. The integrative project outcomes include establishing new molecular tools with improved precision to detect onset and attenuate the progression of HFpEF as well as identify novel therapeutic targets for Veterans suffering from this devastating HF syndrome. In this project, a large animal model of LVPO induced HFpEF will be utilized in order to perform functional (LV regional myocardial stiffness) and exercise studies as well as miR profiling. The guiding hypothesis is that a setpoint shift in a cassette of miRs that regulate the ECM/fibroblast activation process causes a refractory form of HFpEF, defined by a persistent HFpEF phenotype despite removal of the LVPO stimulus. In a parallel set of studies, it will be demonstrated that a standardized exercise regimen will prevent the emergence of this profibrotic miR signature and in turn refractory HFpEF. These studies will provide the foundation for the development of novel diagnostics to provide early detection and moreover provide the foundation for a novel therapeutic direction for the restoration of myocardial plasticity with HFpEF. In this project, the guiding hypothesis is that a key molecular event in the development of HFpEF is the loss of post-transcriptional control by a specific cassette of miRs that regulate ECM homeostasis and fibroblast activation, which results in a refractory form of HFpEF. Integrating a standardized exercise protocol during the progression of HFpEF will prevent this loss of miR post-transcriptional control, attenuate ECM accumulation and fibroblast activation, and thereby prevent the development of a refractory HFpEF phenotype.