Background: Atrial fibrillation (AF) is a frequent complication of acute myocardial infarction (AMI), with reported incidence of 7% to 18%. The incidence of congestive heart failure, in-hospital mortality, and long-term mortality is higher in AMI patients with AF than in AMI patients without AF. P wave duration on signal-averaged ECG (PWD) and P wave dispersion on standard ECC (Pd) are noninvasive markers of intra-atrial conduction disturbances, which are believed to be the main electrophysiological cause of AF. Methods: In the present study we invest(gated prospectively whether P wave duration on SAECG and P wave dispersion on standard ECG can predict development of AF in a group of patients with AMI. One hundred and thirty patients 100 men and 30 women, aged 56.9 +/- 12) with AMI were investigated. PWD, Pd, their clinical and hemodynamic characteristics were collected. Results: During the observation up to 14 days, 22 patients (16.9%) developed AF. Univariate analysis variables associated with development of AF: age > 65 years, Killip class III-IV, PWD > 125 ms, and Pd > 25 ms. Stepwise logistic regression analysis showed that age > 65 years, PWD > 125 ms, and Pd > 23 ms were independently associated with AF. Conclusions: PWD and Pd both measured in a very early period of AMI are useful in predicting AF.