BACKGROUND: Left atrial (LA) size and function change with chronically increased left ventricular (LV) filling pressures. It remains unclear whether these variations in LA parameters can predict new-onset atrial fibrillation (AF) in asymptomatic patients with aortic stenosis (AS). METHODS: Data were obtained in asymptomatic patients with mild-to-moderate AS (2.5≤ transaortic Doppler velocity ≤4.0m/s), preserved LV ejection fraction (EF), no previous AF, and were enrolled in the Simvastatin and Ezetimibe in Aortic Stenosis study. Peak-aortic velocity, LA(max) volume & LA(min) volume were measured by echocardiography. LA conduit (LA(con)) volume was defined as LV stroke volume-LA stroke volume. LA function was expressed as LA-EF (LA(max)-LA(min) volume/LA(max)). RESULTS: In the 1159 patients included, new-onset AF occurred in 71 patients (6.1%) within a mean follow-up of 4.2±0.9years. Mean age was 66±9.7years, aortic valve area index 0.6±0.2cm(2)/m(2), LV mass 99.2±29.7g/m(2), LA(max) volume 34.6±12.0mL/m(2), LA(min) volume 17.9±9.3mL/m(2), LA-EF 50±15% and LA(con) volume 45±21mL/m(2). Baseline LA(min) volume predicted new-onset AF in Cox multivariable analysis (HR:2.3 [95%CI:1.3-4.4], P