Background Elite endurance training is characterised by a high-volume load of the heart and has been associated with atrial fibrillation (AF) in middle-aged men. We compared left atrial (LA) remodelling among elite athletes engaged in sports, categorised as having low, intermediate, and high cardiac demands. Methods This cross-sectional echocardiographic study of healthy elite athletes evaluated LA size and function measured as LA maximum volume (maxLAVi) and contraction strain. Athletes were grouped according to the cardiac demands of their sport (low, intermediate, high). Morphological measures were indexed to body surface area and reported as least square means; differences between groups were reported with 95% CIs. Results We included 482 elite athletes (age 21±5 years (mean±SD), 39% women). MaxLAVi was larger in the high group (28.4 mL/m 2) compared with the low group (20.2 mL/m 2; difference: 8.2, CI 5.3 to 11.1 mL/m 2; p<0.001), where measurements in men exceed those in women (26.4 mL/m 2 vs 24.7 mL/m 2; difference 1.6 mL/m 2; CI 0.3 to 2.9 mL/m 2; p=0.0175). In the high group, LA contraction strain was lower compared with the low group (-10.1% vs -12.9%; difference: 2.8%; CI 1.3 to 4.3%; p<0.001), and men had less LA contraction strain compared with women (-10.3% vs -11.0%; difference 0.7%; CI 0.0 to 1.4%; p=0.049). Years in training did not affect maxLAVi or LA contraction strain. Conclusion MaxLAVi was higher while LA contraction strain was lower with increased cardiac demands. MaxLAVi was larger, and LA contraction was lower in men compared with women. Whether these sex-based differences in LA remodelling are a precursor to pathological remodelling in male athletes is unknown.