Background: We investigated P wave dispersion and left atrial appendage (LAA) function for predicting atrial fibrillation (AF) relapse, and the relationship between P wave dispersion and LAA function. Methods: Sixty-four consecutive patients with AF lasting less than or equal to3 months were evaluated to predict the recurrence after successful cardioversion. P wave duration and dispersion were measured in a 12-lead electrocardiograph (ECG). The size and function of the left atrium (LA) and LAA were assessed by transthoracic and transesophageal echocardiography. Results: After 6 months, 28 patients experienced recurrent AF and 36 remained in sinus rhythm. There was no difference between patients with and without recurrence in gender, age, underlying heart disease, AF patterns, left ventricular function, and maximum LAA area. AF duration greater than or equal to5 days, LA size greater than or equal to45 mm, maximum P wave duration greater than or equal to112 ins, P wave dispersion greater than or equal to47 ms, spontaneous echo contrast, minimum LAA area greater than or equal to 166 mm(2), and LAA emptying velocity <36 cm / see were univariate predictors of recurrence (each P < 0.05). By multivariate analysis, LA size (P = 0.02), P wave dispersion (P < 0.001), and LAA emptying flow (P = 0.01) identified patients with recurrent AF Their positive predictive values were 91, 97, and 72%, respectively. Conclusion: The increased P wave dispersion in addition to the dilated LA and the depressed LAA emptying flow can identify patients at risk of recurrent AF after cardioversion.