Background : Atrial fibrillation(AF) often occurs in Brugada syndrome(BS) and atrial vulnerability measured by increased atrial conduction time was reported. However, dispersion of atrial repolarization has not been known in these patients. Methods : Monophasic action potentials(MAP) were recorded from four sites of right atrial myocardium and analyzed in 11 patients(M/F 10/1, 40짹9 years) with BS and in 10 controls(M/F 8/2, 35짹8 years) with paroxysmal supraventricular tachycardia. There were no history of AF in both groups. MAPs were recorded during atrial pacing at a drive cycle length of 600msec after three minutes of continuous pacing. MAPD90 was measured from onset to 90% of MAP repolarization. Maximum and minimum MAPD90 were obtained from all patients and the dispersion of MAPD90(D-MAPD90) was defined as the difference between maximum and minimum MAPD90. Inducibility of AF and repetitive atrial firing(occurrence of two or more successive atrial electrograms induced by atrial premature stimulation) was also studied with extrastimuli until atrial effective refractory period. Results : The MAPD90 was not significantly different between two groups (24542ms in BS and 22824ms in control group, p=ns), but D-MAPD90 was significantly increased in patients with BS versus control group (69.135.0ms and 41.410.3ms, p<0.05). AF was induced in 6 and repetitive atrial firing in 4 patients with BS but in none of the control subjects. Conclusions : Dispersion of MAPD90 was significantly increased in BS, suggesting that the heterogeneity of atrial repolarization may contribute for development of atrial fibrillation in patients with BS.