Sinus venosus defect (SVD) is an uncommon type of interatrial communication in which cardiac magnetic resonance (CMR) is increasingly used as an alternative imaging modality. The goal of this study was to determine the accuracy of CMR in patients with SVD compared with surgical findings. The diagnostic studies and operative reports of all patients who had CMR followed by surgical repair of SVD (n = 16) from 1996 to 2005 were reviewed and discrepancies were recorded. CMR studies included assessment of anatomy (evaluated by a combination of gradient echo cine, spin echo, and gadolinium-enhanced three-dimensional magnetic resonance angiography), ventricular volumes and function, and flow measurements. The median age at CMR was 14 years (range, 0.4-42). Compared with operative findings, there were no major discrepancies with CMR. The SVD was clearly imaged in all patients and 36 anomalously draining pulmonary veins were identified. The median pulmonary-to-systemic flow ratio was 2.4 (range, l.3-4.6). Patients had an average of 1.7 previous diagnostic tests (range, 1-3; 19 transthoracic echo, 5 catheterizations, and 3 transesophageal echo). Before CMR, SVD was diagnosed in 1 patient, suspected in 7, and not suspected in 8. Additional unsuspected findings identified by CMR included malposition of septum primum (n = 2), left superior vena cava to coronary sinus (n = 2), and aortic arch anomalies (n = 2). CMR accurately depicts SVD anatomy and associated anomalous pulmonary venous drainage, provides quantitative information on the hemodynamic burden, and reveals additional cardiovascular abnormalities. This experience indicates that CMR provides the information necessary for surgical planning of SVD repair.