Background: Left ventricular (LV) mass is an important predictor of morbidity and mortality. However, the accuracy of 2D echocardiographic LV mass measurements is limited because acquiring anatomically correct apical views is often difficult. New echocardiography machines include version of real-time, three-dimensional echocardiography (RT3DE) capabilities which allow for the single beat acquisition of the mass of the LV and incorporate algorithms for automated border detection. We tested the hypothesis that LV mass could be measured more accurately from RT3DE data sets, which allow offline selection of nonforeshortened apical views, by comparing 2D and RT3D measurements against cardiac MR (CMR) measurements. Methods: Echocardiographic imaging was performed (Acuson SC2000) in 34 patients referred for CMR(1.5-T, Avanto). Apical 2- and 4-chamber views and RT3D data sets were acquired and analyzed by 2 independent observers. The RT3DE analysis was performed with a pre-equipped program (eSieScan workflow protocol) run on the SC2000 system. In both 2D and RT3D images, LV long axis was measured; endocardial and epicardial boundaries were traced and mass was calculated by use of the biplane method of disks. Results: Pearson���s correlation showed close correlation of LVMI according to RT3DE and CMR (r=0.89, P-value < 0.0001). Bland-Altman analysis showed reasonable limits of agreement. Both interobserver and intraobserver variability of 3D measurements of LV mass showed excellent agreement. Conclusions: RT3DE provides the basis for accurate and reliable measurement of LV mass.