1. An automated computer-implemented method for reorienting ECT myocardial perfusion images of a left ventricle (LV) of a heart, the method comprised of: receiving variously oriented tomographic images of a reconstructed volume of a heart; determining or receiving the LV long-axis and LV center (x c , y c , z c ) and determining or receiving axial limits (z apex and z base ) of the LV based on the tomographic images; determining or receiving the endocardial surface of the LV based on the tomographic images; determining a reorientation slice range based on the center and axial limits of the LV; receiving or reconstructing a number of slices (N) within the reorientation slice range; for each slice i=1 to N, determining a center coordinate x[i], y[i] based on the endocardial surface and the area of the slice i within a reorientation slice range coordinate system; determining translation values Δx i , Δy i and rotation values θ x , θ y based on the center coordinates x[i=1 to N], y[i=1 to N] to reorient the long axis of the LV to the z-axis and its origin of a reference Cartesian coordinate system; and automatically reorienting and realigning the tomographic images based on the translation values and rotation values to obtain reoriented ECT images reoriented and realigned to the long axis of the left ventricle.