The value of transesophageal echocardiography in preoperative anatomic mapping of a leaking mitral valve is established. Apart from perforated, hypermobile or restricted leaflets, a dilated annulus is a common cause of mitral regurgitation. Based on multiple plane imaging and a simplified model in which the annulus was approximated ellipsoid, the dimensions of the normal major and minor axes were measured at three specific time points during the heart cycle. Based on reproducibility and dimensional calculations, standardized annular dimensional reference values are suggested.