The aim of this prospective study was to evaluate the incremental value of left atrial (LA) function for the prediction of risk for first atrial fibrillation (AF) or atrial flutter. Maximum and minimum LA volumes were quantitated by echocardiography in 574 adults (mean age 74 +/- 6 years, 52% men) without a history or evidence of atrial arrhythmia. During a mean follow-up period of 1.9 +/- 1.2 years, 30 subjects (5.2%) developed electrocardiographically confirmed AF or atrial flutter. Subjects with new AF or atrial flutter had lower LA reservoir function, as measured by total LA emptying fraction (38% vs 49%, p <0.0001) and higher maximum LA volumes (47 vs 40 ml/m(2), p = 0.005). An increase in age-adjusted risk for AF or atrial flutter was evident when the cohort was stratified according to medians of LA emptying fraction (< or =49%: hazard ratio 6.5, p = 0.001) and LA volume (> or =38 ml/m(2): hazard ratio 2.0, p = 0.07), with the risk being highest for subjects with concomitant LA emptying fractions < or =49% and LA volume > or =38 ml/m(2) (hazard ratio 9.3, p = 0.003). LA emptying fraction (p = 0.002) was associated with risk for first AF or atrial flutter after adjusting for baseline clinical risk factors for AF or atrial flutter, left ventricular ejection fraction, diastolic function grade, and LA volume. In conclusion, reduced LA reservoir function markedly increases the propensity for first AF or atrial flutter, independent of LA volume, left ventricular function, and clinical risk factors.