Background: Prolonged endurance exercise is associated with an increased risk of atrial fibrillation (AF) in men. Left atrial (LA) dilation is a marker of pathological atrial remodeling and associated with AF in the general population. In athletes, however, atrial dilation is part of a physiological response to exercise, and functional parameters may help separate physiological from pathological atrial remodeling in this group. LA mechanical dispersion (LA MD) is a novel marker of LA mechanical dyssynchrony associated with AF in the general population. The associations between prolonged endurance exercise, LA MD and AF are yet to be investigated. Purpose: To investigate LA MD in male veteran athletes who had regularly participated in an annual 54-kilometer cross-country (XC) ski race in Norway with and without paroxysmal AF and to investigate the ability of LA MD to identify veteran athletes with paroxysmal AF. Methods: Two hundred and ninety-three men from four groups, veteran XC skiers with (n=57) and without (n=87) AF, and men from a non-athletic population with (n=61) and without AF (n=88) underwent an echocardiographic exam while in sinus rhythm. Using speckle-tracking echocardiography, LA strain was measured in each of the six atrial segments in an atrial-focused apical four-chamber view. We defined LA MD as the standard deviation of time-to-peak strain (SD-TPS) and report the average from three consecutive loops. Results: XC-skiers (mean age 70.9 ± 5.7 years) reported an average of 40-50 years of regular endurance exercise and an average of 16 completed annual Birkebeiner XC ski races. LA volumes were associated with both AF and athletic status (p<0.001). SD-TPS was associated with AF (p<0.001), but not with athletic status (p=0.173). We found no significant trend between years of endurance exercise and SD-TPS in individuals without AF (p=0.846). SD-TPS did not add incremental value in identifying athletes with AF in addition to clinical markers, QRS width, LA volume, and LA reservoir strain (p=0.056). Conclusion: LA MD was associated with paroxysmal AF regardless of athletic status. However, it was not associated with years of performing endurance exercise, suggesting LA MD could be a promising marker of pathological atrial remodeling in endurance athletes, less affected by physiological exercise-induced atrial remodeling than absolute volumetric measurements. We found no incremental value of LA MD in identifying veteran athletes with paroxysmal AF when LA reservoir strain was included in the model.