Background: It is known that overt diabetes as well as chronic hyperglycaemia can lead to atrial fibrillation. A P wave dispersion (PWD) represents heterogeneity in atrial refractoriness.,Aim: To investigate PWDs in patients with pre-diabetes.,Method: Based on the results of examinations, 84 pre-diabetic patients (the pre-DM group; 50 female, 34 male; mean age 54 +/- 8.6 years) who had no overt diabetes, coronary artery disease or hypertension, whose fasting blood glucose was higher than 100 mg/dL and/or whose 2 h glucose concentrations on an oral glucose tolerance test was in the range of 140 to 199 mg/dL, and 48 healthy volunteers (the non-DM group, 30 female, 18 male; mean age 51.7 +/- 7.3 years) with no illnesses, were enrolled in this study. Standard 12-lead electrocardiograms of all patients were taken at 50 mm/s and 20 mm/mV standardisation. Maximum (P-max) and minimum (P-min) P-wave durations were measured. The PWD was defined as the difference between P-max and P-min.,Results: The P-max and PWD values were significantly higher in pre-DM compared to non-DM (104 +/- 13 ms vs 98 +/- 12 ms; p < 0.05, 42 +/- 13 ms vs 34 +/- 11 ms; p < 0.01 respectively). A positive correlation was found between PWD and fasting blood glucose (r = 0.32; p < 0.01). There was no correlation between PWD and HbA1c levels (r = 19; p > 0.05). Multivariate regression analysis showed no relationship between PWD and age, left atrial diameter, E, A, E/A or HbA1c. However, there was a relationship between PWD and fasting blood glucose.,Conclusions: The P-max PWD are increased in pre-diabetic patients who have no coronary artery disease, hypertension or left ventricular hypertrophy.