To assess the utility of cardiac magnetic resonance (MR) imaging in the diagnosis of constrictive pericarditis (CP). This study was approved by the institutional review board, with a waiver of informed consent. A total of 42 consecutive patients (mean age, 55 ± 16 years; 3 women, 39 men) with CP treated with pericardiectomy who had undergone cardiac MR before surgery were evaluated retrospectively. An additional 21 patients were evaluated as a control group; of these, 10 consecutive patients received cardiac MR for reasons other than suspected pericardial disease, and 11 consecutive patients had a history of pericarditis but no clinical suspicion of pericardial constriction. MR imaging parameters were analyzed independently and with a decision tree algorithm for usefulness in the prediction of CP. Catheterization data were also reviewed when available. A model combining pericardial thickness and relative interventricular septal (IVS) excursion provided the best overall performance in prediction of CP (C statistic, 0.98, 100% sensitivity, 90% specificity). Several individual parameters also showed strong predictive value in the assessment of constriction, including relative IVS excursion (sensitivity, 93%; specificity, 95%), pericardial thickness (sensitivity, 83%; specificity, 100%), qualitative assessment of pathologic coupling (sensitivity, 88%; specificity, 100%), diastolic IVS bounce (sensitivity, 90%; specificity, 85%), left ventricle area change (sensitivity, 86%; specificity, 100%), and eccentricity index (sensitivity, 86%; specificity, 90%; all P < 0.001). Strong agreement was observed between catheterization and surgical findings of constriction (97%). Cardiac MR provides robust quantitative and qualitative analysis for the diagnosis of CP.