Although recommended by the current guidelines, 3D echocardiographic (3DE) quantification of the cardiac chambers in clinical practice has been lagging, because of time-consuming analysis. We recently validated an automated algorithm that measures left atrial (LA) and left ventricular (LV) volumes and ejection fraction (EF). This study aimed to determine its accuracy and reproducibility in a multicenter setting. 180 patients underwent 3DE imaging (Philips) at 6 sites. Images were analyzed using automated HeartModel (HM) software with endocardial border correction when necessary, and also by conventional manual tracing. Measurements were performed independently by each site and by the Core Laboratory (CL), whose measurements were used as a reference. Inter-technique comparisons included HM measurements by the sites with and w/o corrections against manual tracing by CL. Intra-technique comparisons included HM measurements by the sites against those by CL (with and w/o corrections, respectively). Inter-technique comparison w/o corrections showed strong correlations, with the automated technique slightly underestimating LV volumes. Corrections were either unnecessary or minimal in most patients, and affected the measurements minimally. Intra-technique comparisons with corrections showed better correlations and smaller biases than the inter-technique comparison. All automated measurements with corrections were more reproducible than manual measurements. Automated volumetric analysis of left-heart chambers is an accurate alternative to conventional methodology, which yields almost the same values across laboratories and is more reproducible. This technique may contribute towards full integration of 3DE quantification into clinical routine.