Echocardiographic assessment of systolic left ventricular (LV) function in patients with severe mitral regurgitation (MR) undergoing mitral valve (MV) repair can be challenging because the measurement of ejection fraction (EF) or fractional area change (FAC) in pathological states is of questionable value. The aim of our study was to evaluate the usefulness of the pre-operative Tei Index in predicting left ventricular EF or FAC immediately after MV repair. One hundred and thirty patients undergoing MV repair with sinus rhythm pre- and post-operatively were enrolled in this prospective study. Twenty-six patients were excluded due to absence of sinus rhythm post-operatively. Standard transesophageal examination (IE 33, Philips, Netherlands) was performed before and after cardiopulmonary bypass according to the guidelines of the ASE/SCA. FAC was determined in the transgastric midpapillary short-axis view. LV EF was measured in the midesophageal four- and two-chamber view. For calculation of the Tei Index, the deep transgastric and the midesophageal four-chamber view were used. Statistical analysis was performed with SPSS 17.0. values are expressed as mean with standard deviation. LV FAC and EF decreased significantly after MV repair (FAC: 56±12% vs. 50±14%, P<0.001; EF: 58±11 vs. 50±12Έ P<0.001). The Tei Index decreased from 0.66±0.23 before MV repair to 0.41±0.19 afterwards (P<0.001). No relationship between pre-operative Tei Index and post-operative FAC or post-operative EF were found (FAC: r=-0.061, P=0.554; EF: r=-0.29, P=0.771). CONCLUSIONS Pre-operative Tei Index is not a good predictor for post-operative FAC and EF in patients undergoing MV repair.