Objective : To assess the acute and intermediate changes in mitral regurgitation (MR) severity after transcatheter aortic valve implantation (TAVI) with the CoreValve Revalving SystemTM (CRS). Background: Following surgical aortic valve replacement, improvement in MR is reported in 27-82% of the patients. The changes in MR severity following CRS implantation are unknown. Methods: Transthoracic echocardiography was performed in 79 consecutive patients before and after treatment, and at the first outpatient visit. Left ventricular dimensions and ejection fraction (LVEF), left atrial (LA) size, and aortic gradient were measured. MR was assessed by color flow mapping and was graded as none, mild, moderate, or severe. It was defined as organic or functional. The depth of CRS implantation was measured by angiography. Results: Post-treatment, the mean gradient decreased from 48 +/- 16 mm Hg to 9 +/- 5 mm Hg (P < 0.0001). There was no significant change in the left ventricular dimensions, LA size, and LVER MR pretreatment was mild, moderate, or severe in 57%, 18%, and 1% of the patients, respectively. It was defined as organic in 27 patients (36%) and functional in 27 patients (36%). The degree of MR remained unchanged in 61% of the patients, improved in 17%, and worsened in 22%. MR improvement was associated with a lower baseline LVEF (P = 0.02). There was no association between the changes in MR severity and the depth of CRS implantation. Conclusions: Most patients who underwent TAVI had some degree of MR. Overall there was no change in the degree of MR post-treatment. Patients in whom MR improved had a lower LVEF at baseline. (C) 2009 Wiley-Liss, Inc.