A quantitative characterization of the shape of the right ventricle (RV) of the heart is needed for accurate modeling of the mechanics of the ventricle as well as for better measuring the volume of the ventricle from technologies such as 2D ultrasound, bi-planar ventriculography, and sonomicrometry. A technique was thus developed for modeling RV shape. First, a high-resolution MR image set was obtained of the freshly excised lamb heart under various passive pressurizations of both ventricles ranging from 5 to 30 cmH2O simulating end-diastole in the beating heart. Typically, 2-3 full images were obtained for each heart. Images were obtained with a multislice spin-echo T1-weighted sequence with the slice plane orientation early equal to the short-axis view of the heart. A 3D characterization of shape was obtained by first characterizing inter-slice changes in shape and orientation and then characterizing the shape of a single representative slice. The slice chosen to represent the RV was in the region directly below the tricuspid valve since it is both near to the apex-base center of the RV and has the greatest size. Intuitive deformations were applied to an initial circular arc anchored at the endpoints of the freewall and initially passing through a point near the center of the freewall contour, so as to best match the true freewall contour.