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Atrial septal defect (ASD) flow can be measured indirectly by velocity-encoded cardiovascular magnetic resonance (veCMR) of the pulmonary artery and aorta. Imaging the secundum ASD en face could potentially enable direct flow measurement and provide valuable information about ASD size, shape, location, and proximity to other structures.Forty-four patients referred for possible transcatheter ASD closure underwent a comprehensive standard evaluation, including transesophageal and/or intracardiac echocardiography and invasive oximetry. CMR was performed in parallel and included direct en face veCMR after an optimal double-oblique imaging plane was determined that accounted for ASD flow direction and cardiac-cycle interatrial septal motion. ASD flow measured by direct en face veCMR correlated better with invasive oximetry than indirect (pulmonary artery and aorta) veCMR (r=0.80 versus r=0.66). Additionally, 95% limits of agreement were narrower (±3.9 versus ±5.1 L/min). En face veCMR determined that defects usually were eccentrically shaped (major/minor axis length >1.5) rather than circular, with 16% having extreme eccentricity (major/minor >2.0). Overall, ASD size by both veCMR and intracardiac echocardiography correlated with final device size; however, in small to medium defects (<3 cm2) and extremely eccentric defects, veCMR correlated better with final device size than did intracardiac echocardiography. Importantly, CMR identified additional information in 9 patients (20%) that altered clinical management. Specifically, en face veCMR detected additional defects (n=3), large ASD with insufficient rim tissue (n=2), and sinus venosus defect with anomalous pulmonary vein (n=1). Cine and/or morphological imaging detected interrupted inferior vena cava (n=2) and sinus of Valsalva aneurysm (n=1).En face veCMR with an optimized imaging plane can determine ASD flow, size, and morphology. CMR provided information incremental to comprehensive standard evaluation that altered clinical management in 20% of patients.