The tricuspid annulus (TA) is a complex structure that has been rarely evaluated. Three-dimensional transesophageal echocardiography (3D-TEE) gives us the unique opportunity to evaluate TA shape and dimensions. 3D dynamic volumetric datas of the TA were acquired by TEE using a matrix array transducer (X7-2t, Philips) in 184 patients. Multiplanar reconstructions were performed offline using a dedicated software (QLab7, Philips). Long-axis (LA) diameter, short-axis (SA) diameter and the area of the TA at the time of its maximal opening were measured. The eccentricity index (EI) of the TA was defined as LA/SA and TA orientation as the angle between the interatrial septum axis (aortic valve on the top at 0°) and the LA in the surgical view. Morphology of TA was more often oval (EI=1.35±0.22) but shapes were significantly different among indivuals, from circular to oval (EI values from 1 to 2.15). TA dilatation occurred homogeneously in all the directions of the right ventricle free wall as attested by the very good correlation between the TA area and both LA (r=0.89, p<0.0001) and SA (r=0.88, p<0.0001). TA dilatation, as shown by increase in TA area, was associated with a small decrease of EI (r=-0.21, p<0.0001), thus a trend to a more circular TA. All orientations of TA were observed, from 5 to 175° (mean=87°±57°) with a bimodal distribution (most frequently at 40° and 150°). 3D-TEE allowed a good assessment of the TA shape and orientation, which is significantly different among individuals. This method could be interesting to improve assessment of TA dilatation before left-heart valve surgery. Display omitted