PROJECT SUMMARY Heart failure with preserved ejection fraction (HFpEF) continues to pose a major burden to the healthcare system, women are twice as likely as men to develop HFpEF, and no targeted therapies for HFpEF exist. Coronary microvascular dysfunction (CMD), defined as impaired function of the small microvessels within the heart, is a widely prevalent yet poorly understood condition that also predominantly affects women. HFpEF is the most frequently experienced morbid outcome in women with CMD, who are often younger than those with other HFpEF phenotypes. While we and others have shown that HFpEF is present in up to a third of women with CMD, the pathobiology of CMD-related HFpEF remains unclear. CMD leads to chronic myocardial ischemia, which results in an intra-cardiomyocyte metabolic shift towards increased glucose utilization, reduced free fatty acid oxidation, and triglyceride (TG) accumulation in the myocardium – leading to myocardial steatosis, which we have associated with diastolic dysfunction, a pre-HFpEF trait. Because women with CMD are more likely than men to suffer chronic ischemia for longer durations, our central hypothesis is that CMD-related chronic ischemia and subsequent myocardial steatosis are key contributors to the development of HFpEF in women with CMD. Emerging data from our group underscores the importance of chronic inflammatory (i.e. eicosanoid) pathways in governing responses to the ischemic, intra-cardiomyocyte metabolic shifts, and cardiac mechanical stressors that have been implicated in CMD and HFpEF pathophysiology. Therefore, the aims of this Early Stage Investigator R01 application are to: (1) determine the relationship between chronic ischemia and myocardial steatosis and the extent to which myocardial steatosis mediates associations between ischemia and pre-clinical HFpEF in CMD; and, (2) identify specific eicosanoid molecules that underlie risk for CMD-related myocardial steatosis, pre-clinical HFpEF traits, and clinical HFpEF. In a prospective cohort of 220 CMD women undergoing comprehensive cardiac magnetic resonance (CMR) imaging and spectroscopy, we will determine clinical HFpEF status and quantify: (i) myocardial TG content and steatosis; (ii) chronic ischemia burden, and (iii) pre-clinical CMR HFpEF traits to relate chronic ischemia with myocardial steatosis. Plasma biosamples from the cohort will undergo high-throughput analyses to identify distinct eicosanoid profiles associated with myocardial steatosis. An exploratory analysis with 18F-FDG PET will relate the eicosanoid profiles to myocardial-specific inflammation. The eicosanoid profiles will also be tested for incident HFpEF in a large community cohort with over a decade of HFpEF outcomes. Understanding the role of cardiac steatosis with respect to CMD-related ischemia, inflammation, and HFpEF traits promises to reveal novel targets for preventing and treating HFpEF, especially in women.