BACKGROUND: Racial and ethnic differences in diabetic cardiomyopathy (DbCM) exist, with black and Hispanic participants showing poorer health status. It remains unclear whether these differences affect the natural progression of the disease. We aimed to evaluate disease progression in individuals with DbCM, as well as racial differences in the response to AT-001. METHODS: A total of 625 participants with DbCM were randomised to either placebo or AT-001 and followed for 15 months. The primary outcome was change in peak oxygen uptake (peak VO2) and secondary outcomes included Kansas City Cardiomyopathy Questionnaire (KCCQ) and Physical Activity Scale for the Elderly scores. Analyses were stratified by race and ethnicity (black, Hispanic, white). RESULTS: Black and Hispanic participants who received placebo experienced greater declines in peak VO2 (-0.74 and -1.67 mL/kg/min, respectively) compared with white participants (-0.23 mL/kg/min, p=0.005). AT-001 demonstrated a non-statistically significant trend towards slower declines in peak VO2 in black and Hispanic participants (-0.31 and -0.62 mL/kg/min, p=0.29, respectively). Black participants who received placebo had the largest declines in most KCCQ scores. CONCLUSION: Black and Hispanic participants with DbCM experienced faster disease progression, with black participants showing the most pronounced functional and quality of life declines. The effect of AT-001 on peak VO2 changes was not statistically significant with similar effects between racial and ethnic groups (NCT04083339). TRIAL REGISTRATION NUMBER: NCT04083339.