Backgrounds and Purposes:It is uncertain whether self-terminating episodes of paroxysmal atrial fibrillation(PAF) alter atrial mechanical function during normal sinus rhythm. This study was to assess the initial left atrial(LA) mechanical changes after episode of PAF with transthoracic(TTE) and transesophageal echocardiography(TEE) that predict development of persistent AF. Methods:Twenty-six consecutive patients(mean age, 59짹10.6years;12 males) with newly diagnosed lone AF(mean duration of symptom, 2.5days;range 1day-10days) who converted to sinus rhythm spontaneously were studied prospectively. TTE and TEE were performed after 1-2 days of spontaneous sinus conversion and parameters associated with LA function and dimension were measured including LA and left atrial appendage(LAA) Fractional area change(FAC)(figure, maximum and minimum LAA area), fractional shortening(FS), ejection force(EF) and P wave to LAA ejection interval. The patients were followed up for the recurrence of AF after a year. Results:AF recurred in 11(42.3%) patients after a mean time of 12.9짹4.3months. Multiple regression analysis indicated that FAC of LAA was an independent predictor of AF recurrence,(32.1 짹 9.0% vs 49.9 짹 20.6%, p<0.01 ) and revealed no significant differences in LA size parameters or LA mechanical function parameters including LA FS and EF between patients with and without AF recurrence.Conclusion:FAC of LAA may be considered to be an independent predictor of development of recurrent and persistent AF.