PROJECT SUMMARY/ABSTRACT It is well established that there are racial disparities in mortality rates and postoperative outcomes following coronary artery bypass graft with or without valvular replacement / repair (CABG/VR) surgery, particularly in Non-Hispanic Black Americans compared to Non-Hispanic White Americans. Hospital quality and a lack of guideline-concordant care (e.g., insulin infusions, timely antibiotics) are significant contributors; however, a large fraction of this racial disparity remains unexplained. Sleep, circadian rhythm disruption, and impaired glucoregulation may play a role in post-CABG/VR health disparities in Non-Hispanic Black Americans. These disruptions may result in prolonged length of stay, postoperative convalescence, impaired immune function, and cardiovascular morbidity and mortality. Therefore, the purpose of this descriptive study is to examine sleep and circadian rhythm characteristics and the relationships between sleep, circadian rhythm, and glucoregulation among adults in the intensive care unit postoperative CABG/VR surgery. In Aim 1, we will determine between- and within-person associations of sleep, circadian rhythm and glucoregulation associations among 30 adults post-coronary artery bypass graft with or without valvular surgery (50% non-Hispanic Black and 50% non- Hispanic White). Sleep and circadian characteristics will be described through the timing of behavioral (actigraphy) measures. In Aim 2, we will compare sleep, circadian rhythm characteristics, and glucoregulation between 15 individuals identifying as Non-Hispanic Black to 15 individuals identifying as Non-Hispanic White post-coronary artery bypass graft with or without valvular surgery. Our central hypothesis is that higher sleep and circadian disruption are associated with poorer glucoregulation and that there are sleep, circadian, and glucoregulation racial disparities among individuals post-CABG/VR. The proposed F31 study and training plan will provide a strong foundation in sleep and circadian rhythm health disparities. Promoting sleep and circadian rhythm stability post-surgery through behavioral modifications may improve glucoregulation by reducing insulin resistance, improving insulin sensitivity, and other short- and long-term postoperative outcomes in a population where such clinical gains may otherwise be difficult to achieve. This study will provide information on a novel potential contributor to racial disparities in coronary artery post-operative outcomes in the ICU where it is critical to optimize glucoregulation. Additionally, these results will provide preliminary evidence to inform future longitudinal and intervention studies to improve glucoregulation and postoperative outcomes in this understudied population.