1. Apparatus for automatically identifying the long axis of the left ventricle from SPECT data acquired during a nuclear medicine study of a patient's heart, comprising: computer means for reconstructing and selecting, from said SPECT data and without additional input from a human technician, a single slice of the left ventricle, which single slice is assumed to be a representative transverse slice of the left ventricle; computer means for defining, without additional input from a human technician, a reorientation axis which passes through the center of said single slice and is assumed to be intersected by the long axis of the left ventricle; computer means for reconstructing, without additional input from a human technician, and from said SPECT data and along said reorientation axis, a sagittal slice of the left ventricle; and computer means for defining, without additional input from a human technician, an axis which passes through the center of said sagittal slice and is assumed to be the long axis of the left ventricle.