Background: Percutaneous mitral valve repair (PMVR) is increasingly performed in patients with severe mitral regurgitation (MR). Post-procedural MR grading is challenging and an unsettled issue. We hypothesised that the direct planimetry of vena contracta area (VCA) by 3D-transoesophageal echocardiography allows quantifying post-procedural MR and implies further prognostic relevance missed by the usual ordinal scale (grade I-IV). Methods: Based on a single-centre PMVR registry containing 102 patients, the association of VCA reduction and patients' functional capacity measured as six-minute walk distance (6 MW) was evaluated. 3D-colour-Doppler datasets were available before, during and 4 weeks after PMVR. Results: Twenty nine patients (age 77.0 +/- 5.8 years) with advanced heart failure (75.9% NYHA III/IV) and severe degenerative (34%) or functional (66%) MR were eligible. VCA was reduced in all patients by PMVR (0.99 +/- 0.46 cm(2) vs. 0.22 +/- 0.15 cm(2), p < 0.0001). It remained stable after median time of 33 days (p = 0.999). 6 MW improved after the procedure (257.5 +/- 82.5 m vs. 295.7 +/- 96.3 m, p < 0.01). Patients with a decrease in VCA less than the median VCA reduction showed a more distinct improvement in 6 MW than patients with better technical result (p < 0.05). This paradoxical finding was driven by inferior results in very large functional MR. Conclusions: VCA improves the evaluation of small residual MR. Its post-procedural values remain stable during a short-term follow-up and imply prognostic information for the patients' physical improvement. VCA might contribute to a more substantiated estimation of treatment success in the heterogeneous functional MR group.