OBJECTIVE: To compare two methods of mitral annular nonplanarity: the mathematically calculated annular height-to-commissural width ratio (AHCWR) and the echocardiographically derived nonplanarity angle. DESIGN: Prospective. SETTING: Tertiary care university hospital. INTERVENTIONS: Three-dimensional transesophageal echocardiography. PARTICIPANTS: Patients undergoing mitral valve surgery. MEASUREMENTS AND MAIN RESULTS: Using 3-dimensional transesophageal echocardiography, volumetric datasets were acquired from 22 patients undergoing mitral valve surgery. The intraoperative nonplanarity angle was calculated with Mitral Valve Assessment software (Tomtec GmbH, Munich, Germany). Furthermore, the datasets acquired during 3-dimensional transesophageal echocardiography were exported to Matlab software (MathWorks, Natick, MA), which was used to calculate the AHCWR. The nonplanarity angle was seen to correlate favorably with the AHCWR (r = 0.70). CONCLUSIONS: A favorable correlation was found between the nonplanarity angle and the AHCWR. This suggests that the nonplanarity angle can be used to assess mitral annular nonplanarity in a clinically feasible fashion.