Background: P wave dispersion (PWD) is defined as the difference between the maximum P wave duration (Pmax) and the minimum P wave duration (Pmin) in 12-leads of the surface electrocardiography. The aim of this study was to evaluate the values of PWD during atrial fibrillation (AF) after acute myocardial infarction (AMI). Methods: We prospectively evaluated atrial rhythms of 350 patients (251 males, 99 females) at their first AMI. The measurements included left ventricular ejection fraction (LVEF) and left atrial dimensions (LAD) by means of echocardiography. On admission an ECG was obtained and repeated daily during hospitalization. Results: Fifty patients had AF after AMI. Pmax was significantly higher (140.8±18.9 ms) among patients with AF than patients without AF (106.5±17.3 ms). This was also true about Pmin (66.4±18.3 ms vs. 57.7±15.7 ms), PWD (74.4±20.6 ms vs. 48.7±18.9 ms) and LVEF (35.2±9.4% vs. 39.3±10.9%). Whereas, there was no significant difference between the two groups in respect to LAD (36.5±7.4 mm vs. 35.1± 5.9 mm) Conclusion: Based on the univariate analysis results, Pmin, Pmax, PWD, LVEF and age were significant predictors of atrial fibrillation in patients with first acute myocardial infarction. However, multivariate analysis failed to disclose such independent predictors for atrial fibrillation in these patients.