OBJECTIVE: We sought to compare the feasibility, accuracy, and reproducibility of simultaneous triplane echocardiography for measurements of left ventricular (LV) volumes and ejection fraction (EF) with reference to magnetic resonance imaging (MRI). METHODS: Digital echocardiography recordings of apical LV views with and without intravenous contrast were collected from 53 consecutive patients with conventional 2-dimensional (2D) imaging and with simultaneous triplane imaging. MRI of multiple LV short-axis sections was performed with a 1.5-T scanner. Endocardial borders were manually traced, and LV volumes and EF from 2D biplane echocardiography and MRI were calculated by method of disks. On triplane data, a triangular mesh was constructed by 3-dimensional interpolation and volumes calculated by the divergence theorem. RESULTS: Triplane image acquisition was less time-consuming than 2D biplane. Precontrast feasibility was 72% for triplane and 82% for 2D biplane images, increasing to 98% and 100% with contrast, respectively. Bland-Altman analysis demonstrated LV volume underestimation by echocardiography versus MRI, which was significantly reduced by contrast and triplane imaging. The 95% limits of agreement for EF between echocardiography and MRI narrowed using triplane compared with 2D biplane (precontrast -12.5 to 6.7% vs -17.2 to 9.9%, and with contrast -7.1 to 5.8% vs -9.4 to 6.4%, respectively). At intraobserver and interobserver analysis of 20 patients, limits of agreement for EF narrowed with contrast triplane compared with 2D biplane. CONCLUSION: Simultaneous LV triplane imaging is feasible with simple and rapid image acquisition and volume analysis, and with contrast enhancement it gives accurate and reproducible LV EF measurements compared with MRI.