The PREPARE-MVR study (PRediction of Early PostoperAtive Right vEntricular failure in Mitral Valve repair (MVR) and to explore the associations between/Repair patients) sought to investigate the alterations of right ventricular (RV) contraction pattern in patients undergoing mitral valve replacement/repair (MVR) and to explore the associations between pre-operative RV mechanics and early post-operative RV dysfunction (RVD).We prospectively enrolled 42 patients (63 ± 11 years, 69% men) undergoing open-heart MVR. Transthoracic three-dimensional (3D) echocardiography was performed pre-operatively, at intensive care unit discharge, and 6 months after surgery. The 3D model of the RV was reconstructed, and RV ejection fraction (RVEF) was calculated. We decomposed the motion of the ventricle to compute longitudinal ejection fraction (LEF) and radial ejection fraction (REF). Pulmonary artery catheterization was performed to monitor RV stroke work index (RVSWi). RVEF was slightly decreased after MVR [52 (50-55) vs. 51 (46-54)%; P = 0.001], whereas RV contraction pattern changed notably. Before MVR, the longitudinal shortening was the main contributor to global systolic RV function [LEF/RVEF vs. REF/RVEF; 0.53 (0.47-0.58) vs. 0.33 (0.22-0.42); P < 0.001]. Post-operatively, the radial motion became dominant [0.33 (0.28-0.43) vs. 0.46 (0.37-0.51); P = 0.004]. However, this shift was temporary as 6 months later the two components contributed equally to global RV function [0.44 (0.38-0.50) vs. 0.41 (0.36-0.49); P = 0.775]. Pre-operative LEF was an independent predictor of post-operative RVD defined as RVSWi < 300 mmHg⋅mL/m [OR = 1.33 (95% CI: 1.08-1.77), P < 0.05].MVR induces a significant shift in the RV mechanical pattern. Advanced indices of RV mechanics are associated with invasively measured parameters of RV contractility and may predict post-operative RVD.