Objective:To assess the sensitivity and the specifity of predicting idiopathic AF with P wave duration and P wave dispersion. Methods:The maximum P wave duration and P wave dispersion in 36 patients with idiopathic AF were measured and compared with those of sex - and age - matched healthy subjects. Results:The maximum P wave duration and P wave dispersion were higher in patients with idiopathic Af than in control group. The maximum P wave duration > 110ms or P wave dispersion >40ms was used to differentiate patients from healthy subjects, the sensitivity and the specifity value were 88% vs 82% and 75 % vs 86%, respectively. When the above two parameters were integrated, the sensitivity was 76 %, the specifity 88 %. Conclusion: The maximum P.wave duration and P wave dispersion are simple and practical ECG indexes for idiopathic AF patients.