Abstract Background: Magnetic Resonance Imaging (MRI) and transthoracic echocardiography have been shown to be noninvasive highly sensitive diagnostic tools to identify changes in LV mass and volume. We therefore investigated the effects of mitral valve repair (MVR) on LV function parameters including ejection fraction (EF; %), indices of LV mass (LVMI; g/m2) and volume (LVEDVI, LVESVI; mL/m2) as detected by MRI and echocardiography. Methods: Eight consecutive patients (mean age 53.3 ± 10.0 years) with severe mitral regurgitation (MR; grade III–IV), normal LV function and sinus rhythm were included in this prospective study. Cine MRI and transthoracic M-mode echocardiography were performed pre-operatively, as well as 6 months post-op, to identify changes in EF and in LV mass and volume. Data are given as mean ± standard deviation. Results: Post-op MR was grade 0-I in all patients. Early mortality and late mortality was 0%. EF by either method did not change significantly within the follow-up period. A significant improvement of indices of LV mass and volume was detected by Cine MRI and echocardiography within 6 months following surgery (LVMIMRI: pre-op: 76.3 ± 20.1 vs. post-op: 66.5 ± 14.3, p < 0.05; LVMIEcho: pre-op: 184.2 ± 38.1 vs. post-op: 136.5 ± 28.4, p < 0.05. LVEDVIMRI: pre-op: 119.3 ± 26.0 vs. post-op: 75.4 ± 13.1, p < 0.05; LVEDVIEcho: pre-op: 97.4 ± 28.8 vs. post-op: 69.2 ± 13.1, p < 0.05. LVESVIMRI: pre-op: 44.6 ± 12.0 vs. post-op: 32.5 ± 9.5, p < 0.05; LVESVIEcho: pre-op: 29.3 ± 8.3 vs. post-op: 21.8 ± 4.6, p < 0.05). Conclusions: MRI and echocardiography show a significant reduction of LV volume and mass 6 months after MVR. The data show that for routine follow-up transthoracic M-mode echocardiography provides reliable information for the identification of LV mass and volume regression in patients after MVR.