Images resulting from PET or SPECT studies are usually not oriented along the heart axes and therefore do not cleanly depict the ventricles, the atria, and the myocardial regions supplied by the major coronary arteries.
It is recommended by the AHA  to perform a reorientation of the data so that the long axis of the heart (line apex to the center of the mitral valve) becomes orthogonal to the image planes, and the slice images show short axis cuts. This approach maintains the integrity of the cardiac chambers and the distribution of coronary arterial blood flow to the myocardium. From this orientation slice images at 90° angles can also be generated showing the heart as vertical long axis and horizontal long axis cuts (see illustration below). These correspond to the apical 2-chamber and the apical 4-chamber planes traditionally used in 2D echocardiography.