PURPOSE: To assess ventricular septal motion and quantify the septal configuration in patients clinically suspected of having constrictive pericarditis (CP), and to compare these patients with healthy subjects and with patients who have other diastolic heart abnormalities such as restrictive cardiomyopathy (RCM). MATERIALS AND METHODS: In 41 patients clinically suspected of having CP and 12 healthy subjects, magnetic resonance (MR) imaging yielded information about cardiac morphology and function. On short-axis cine MR images, septal motion was assessed, and the septal and left ventricular free wall (LVFW) radii of curvature were quantified and normalized to end systole. Abnormal diastolic septal motion was expressed in terms of the largest difference in normalized radius between the septum and the LVFW. Analysis of variance was used to identify significant differences in septal shape among subject groups. RESULTS: Left-sided septal flattening was identified in 17 of the 21 patients with surgically proven CP, in none of the 20 patients without CP, and in none of the healthy subjects. CP without septal flattening was present on the left side (n = 1), on the right side (n = 1), and at the atrioventricular grooves (n = 2). Abnormal septal motion yielded a sensitivity of 81% (17 of 21 patients), specificity of 100% (20 of 20 patients), accuracy of 90% (37 of 41 patients), positive predictive value of 100% (17 of 17 patients), and negative predictive value of 83% (20 of 24 patients) in the detection of CP. The maximal difference in normalized radius of curvature between the septum and the LVFW in the patients with CP was significantly different from that in the patients without CP (P <.001) and that in the healthy subjects (P <.001). CONCLUSION: Abnormal diastolic septal motion is a frequent phenomenon of CP. If present in patients suspected of having CP, this finding is helpful in distinguishing CP from RCM.