Although abnormal motion of the interventricular septum (IVS) caused by elevated right ventricular pressure in patients with pulmonary hypertension (PH) is easy to recognize visually, determination of the severity of PH relies on measurements of pulmonary arterial pressure (PAP). We hypothesized that quantitative 3D analysis of regional IVS curvature throughout the cardiac cycle could be used to differentiate patients with different degrees of PH. Cardiac magnetic resonance (CMR) images (Philips 1.5T) were obtained in 14 normal subjects and 30 patients with PH undergoing right heart catheterization, who were divided into 3 subgroups according to mean PAP. Images were used to reconstruct dynamic 3D LV endocardial surfaces, which were analyzed to calculate 3D IVS curvature throughout the cardiac cycle. In normal subjects, IVS curvature was positive, reflecting the convex septal shape and showed little change throughout the cardiac cycle. In patients with PH, IVS curvature was lower, reflecting septal flattening, and fluctuated throughout the cardiac cycle, reflecting the abnormal "bouncing" septal motion. In patients with severe PH, IVS curvature reached negative values, reflecting transient concave septal shape. Dynamic 3D analysis of IVS curvature from CMR images may provide an alternative for noninvasive assessment of severity of PH.