Habitual aerobic exercise is associated with left atrial (LA) enlargement which may increase risk of atrial fibrillation. Patients with LVH and increased LV stiffness may be more predisposed to LA remodeling due to higher LA pressures during exercise. We tested the hypothesis 1 year of aerobic exercise training would increase LA size to a greater extent in patients with LVH than controls. Adults with LVH (n=53) enriched for increased cardiac risk and LV stiffness and control (CON) subjects (n=58) were randomized to one year of high intensity aerobic exercise (ex) or yoga control. LA and LV volumes were measured using 3D echo. Of 111 participants, 83 had complete data available (LVH: 18 exercisers, 10 yoga; CON: 29 exercisers, 26 yoga). Baseline LA volume indices were similar between groups (LVH: 19.8 ± 4.4 mL/m² vs CON: 18.8 ± 4.1 mL/m²; p=0.33). After 1 year, the effects of exercise (p=0.003) and LVH (p=0.001) were each associated with increased LA volume index. More subjects in the LVH/exercise group (33.3%) increased LA size > 5 mL/m² and LA/LV volume ratios > 0.1 compared to the other groups (10% LVH/yoga, 3.4% CON/ex, 3.8% CON/yoga; Chi square p=0.006). In conclusion, 1 year of aerobic training resulted in higher LA volumes in subjects with LVH and LV stiffness compared to healthy subjects. The increase in LA size was greater than changes in LV size suggesting chronic aerobic training in may preferentially affect LA remodeling in subjects with LVH and LV stiffness.