ABSTRACT Myosteatosis is a measure of body composition, which measures the presence and degree of fatty infiltration into the muscle compartment to include deposition around the muscle fibers/bundles, as well as into the muscle tissue itself. Our work on this measure of ectopic fat has shown myosteatosis to be strongly and significantly associated with measures of glucose regulation, independent of visceral and hepatic adiposity. Given the strong links between the glucose dysregulation (i.e. metabolic syndrome and/or diabetes mellitus) and arterial stiffness, as well as left ventricular structure and function, we believe the study of myosteatosis may be particularly relevant as a determinant of heart failure. Compared to non-Hispanic Whites, Hispanic/Latino Americans have significantly higher rates of obesity, cardiometabolic risk factors and type 2 diabetes mellitus (T2DM), resulting in an increased risk for heart failure. To assess the risk factors for different chronic diseases in this burgeoning population, the NIH commissioned the Hispanic Communities Health Study – Study of Latinos (HCHS-SOL). In 2007, this study began recruitment at four different field centers and enrolled over 16,000 Hispanic/Latino Americans from diverse background heritage groups. The HCHS- SOL has now completed two clinic visits and is scheduled to begin enrollment for visit 3 in December 2019. At this visit, the study will update the medical history, obtain fasting blood samples that will be used to measure glucose, insulin and hemoglobin A1C, and will acquire a 2-hour glucose tolerance test. Additionally, the study will conduct the following assessments on the returning participants: 1) objectively measured physical activity and sedentary behavior; 2) peripheral arterial disease by the ankle and toe brachial indices, as well as Doppler waveforms and pulse volume recordings; 3) arterial stiffness by carotid femoral pulse wave velocity and 4) cardiac structure and function by magnetic resonance imaging. This ensemble of measurements can be utilized to assess the pathway from physical activity/sedentary behavior to body composition to cardiometabolic risk to arterial stiffness to cardiac structure and function. Given this, we propose to leverage the existing HCHS-SOL infrastructure and add the acquisition of new computed tomography scans of the abdomen and mid-thigh to obtain measurements of myosteatosis and skeletal muscle mass, as well as subcutaneous, visceral and hepatic adiposity. The goal of this project is to determine the applicability of myosteatosis to the aforementioned pathway among Hispanic/Latino Americans from diverse background heritages, independent of other measures of body composition.