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Atrial fibrillation (AF) is a progressive condition that begins with hemodynamic and/or structural changes in the left atrium (LA) and evolves through paroxysmal and persistent stages. Because of limitations with current noninvasive imaging techniques, the relationship between LA structure and function is not well understood.Sixty-five patients (age, 61.2±14.2 years; 67% men) with paroxysmal (44%) or persistent (56%) AF underwent 3D delayed-enhancement MRI. Segmentation of the LA wall was performed and degree of enhancement (fibrosis) was determined using a semiautomated quantification algorithm. Two-dimensional echocardiography and longitudinal LA strain and strain rate during ventricular systole with velocity vector imaging were obtained. Mean fibrosis was 17.8±14.5%. Log-transformed fibrosis values correlated inversely with LA midlateral strain (r=−0.5, P=0.003) and strain rate (r=−0.4, P<0.005). Patients with persistent AF as compared with paroxysmal AF had more fibrosis (22±17% versus 14±9%, P=0.04) and lower midseptal (27±14% versus 38±16%, P=0.01) and midlateral (35±16% versus 45±14% P=0.03) strains. Multivariable stepwise regression showed that midlateral strain (r=−0.5, P=0.006) and strain rate (r=−0.4, P=0.01) inversely predicted the extent of fibrosis independent of other echocardiographic parameters and the rhythm during imaging.LA wall fibrosis by delayed-enhancement MRI is inversely related to LA strain and strain rate, and these are related to the AF burden. Echocardiographic assessment of LA structural and functional remodeling is quick and feasible and may be helpful in predicting outcomes in AF.