We evaluated ECG-gated SPECT (g-SPECT) in the measurement of absolute left ventricular (LV) volume by comparing it with left ventriculography (LVG) and with cine-MRI. METHODS Projection data from 31 patients were acquired with a three-headed SPECT system in 12 min using a 64 x 64 matrix with 1.5 zoom (1 pixel = 4.27 mm). The R-R interval from simultaneously acquired ECG was divided into eight frames. The end-diastolic and end-systolic volumes (EDV; ESV) and LV mass were assessed by an area-length method with manual delineation of the epi- and endocardial LV borders using midventricular vertical and horizontal long-axis images. The stroke volume, LVEF and cardiac output (CO) were generated from the EDV, ESV and heart rate during the study. The g-SPECT LV values were compared with those of LVG (25 patients) and cine-MRI (18 patients). RESULTS The g-SPECT values correlated well with those from LVG (r = 0.83 to 0.92; p < 0.001) and cine-MRI (r = 0.76 to 0.99; p < 0.001). The g-SPECT technique provides an assessment of LV volumes (EDV, ESV, stroke volume, LVEF, CO, LV mass). CONCLUSIONS Despite potential problems that may cause inaccuracy and require improvements such as an accurate and reproducible automatic edge detection algorithm, g-SPECT has clinical utility in assessing global LV volumes and function.