Thallium-201 gated single-photon emission tomography (GSPET) of myocardium was performed at rest in 18 patients. Images were reconstructed to obtain end-diastolic (ED) and end-systolic (ES) images. The endocardial and epicardial edges of the left ventricle (LV) for the ED and ES images were defined for the mid-ventricular images of the short-axis slices, using a semi-automated method. LV wall thickness was measured for ED and ES images at 10 degrees intervals. Mean LV thickness was derived as the mean of the LV thickness for the three mid-ventricular slices. The systolic thickening (ST) was derived as: mean LV thickness (ES)--mean LV thickness (ED). The systolic thickening ratio (STR) was defined as: ST/mean LV thickness (ED). LV cavity area was measured. The dilation ratio (DR) was defined as: [mean cavity area (ED)--mean cavity area (ES)]/mean cavity area (ED). LV ejection fraction (LVEF) was estimated using technetium-99m gated blood pool study. There was a linear correlation between LVEF and ST (r = 0.85), LVEF and STR (r = 0.77) and LVEF and DR (r = 0.81). There was a strong correlation (r = 0.85) between regional STR and regional percent count increase in 52 segments which did not have perfusion defects. As well as for the evaluation of myocardial perfusion, GSPET images can be of use for the assessment of LV function using an appropriate method for LV edge detection.