ABSTRACT Heart failure (HF), and its subtypes defined by preserved (HFpEF), reduced (HFrEF) or mid-range (HFmrEF) ejection fraction are a major and growing public health problem. The long term goal of this project is to better understand the health disparities regarding HF and define effective preventive measures that may reduce these disparities. We propose to pool data from 10 large longitudinal cohort studies to examine race/ethnic and sex disparities in developing HF, its subtypes, and its prognosis. The harmonized data will include over 130,028 men and women with over 8975 similarly-adjudicated prospective HF outcomes, representing a wide spectrum of ages, race/ethnicities, and geographic regions of the United States. This cross-cohort collaboration will provide a unique opportunity to conduct a comprehensive evaluation of sex and racial/ethnic health disparities in HF. Causal mediation analysis techniques will be used to estimate the degree to which single and multi-factor lifestyle and clinical interventions could potentially reduce health disparities in HF. In our phenomapping aim, we will define unique clinically relevant phenotypes of HF based upon cohort data that is also commonly present in medical records for enhanced generalizability, including age, race/ethnicity, sex, clinical signs, symptoms, biomarkers, ejection fraction, physiologic measures, and co-morbidities; we will also evaluate HF phenotype associations with CVD and all-cause mortality.