Purpose: A planar multi-gated cardiac blood pool acquisition is a non-invasive technique commonly used to measure left ventricular ejection fraction (LVEF).It is essential that the calculation of LVEF be accurate, repeatable and reproducible for serial monitoring of patients. Different processing modes may be used in calculating the LVEF which require various degrees of manipulation.In addition, different operators with varying levels of experience may process the same data set. It is not known whether the inter-operator variability of LVEF values within a single nuclear medicine department has the potential to affect the calculated LVEF and in turn affect patient management. The aim of the study was to determine variability of LVEF values among operators with different levels of experience using two processing modes.Methods: A descriptive cross-sectional study was carried out in a single setting.Four operators with varying levels of experience analysed 120 left anterior oblique projections using manual and automatic processing modes to calculate the LVEF. Inter-and intra-operator correlation was determined.Results: Manual processing showed moderate to strong agreement (r1=0.653) between operators. Automatic processing indicated almost perfect (r1=0.812) inter-operator correlation. Intra-operator correlation demonstrated a trend of decreasing variability between processing modes with increasing levels of experience. Conclusion:Despite the overall inter-operator agreement, significant intraoperator variability was evident in results from operators with less experience.However, the discrepancies were such that the differences in LVEF would not 3 play a role in patient management. It is recommended that automatic processing be used for determining LVEF to limit inter-operator variability.Additionally operator experience should be considered in the absence of standardised processing protocols when different processing modes are available in a single setting.