Abstract: A method for fitting a surface to some portion of a patient's heart. In the method, ultrasound imaging is carried out over at least one cardiac cycle, providing a plurality of images in different image planes made with a transducer at known positions and orientations. An operator selects points on some of the images that correspond to the surface of interest, and a surface is automatically fit to the points in three dimensions, using prior knowledge about heart anatomy to constrain the fitted shape to a reasonable result. The operator reviews the fitted surface, in 3D or alternatively, as intersected with the images. If the fit is acceptable, the process is done. Otherwise, the image processing is repetitively carried out, guided by the fitted surface, to produce additional data points, until an acceptable fit is obtained. The resulting output surface can be used in determining cardiac parameters.