The goal of this observational study is to compare the safety and effectiveness of a 3-steps standardized repair-oriented strategy with annuloplasty only in pediatric patients with mild to moderate mitral valve regurgitation.

The main questions it aims to answer are:

• Can 3-steps standardized repair-oriented strategy improve both left ventricular and mitral valve function in pediatric patients with mild to moderate mitral valve regurgitation?
• Can surgical complications caused by the 3-steps standardized repair-oriented strategy be non-inferior (clinically acceptable) to annuloplasty only? Participants will be assigned to either the Standardized Group (including subvalvular apparatus rehabilitation (leaflet plication if chordae absent on leaflet margin, mal-connected chordae resection if chordae mal-connected to leaflet body, papillary muscle splitting if short chordae or dysplastic or fused papillary muscle etc.), leaflets repair (leaflets plication if functional leaflet prolapse, leaflet cleft closure and patch augmentation for anatomical leaflet defect, etc.) and annuloplasty (posterior annuloplasty for annular dilatation and shallow leaflet coaptation, etc.)) or the Annuloplasty Group (annuloplasty only during mitral repair surgeries. Additionally, echocardiography, electrocardiograms, and measurements of N-terminal pro-brain natriuretic peptide (NT-proBNP) were conducted before the initiation of surgery and at 1 months, 3 months, and 6 months after mitral repair.

Researchers will compare the Standardized Group and the Annuloplasty Group to see if the recurrence rate of moderate to severe mitral valve regurgitation, as assessed by echocardiography after 6 months of surgery, is lower in the former than in the latter.

Inclusion Criteria:

• < 14 years old
• had not undertake mitral valve surgery before
• moderate to severe mitral regurgitation

Exclusion Criteria:

• moderate to severe mitral regurgitation which concommitant with other cardiac malformation which can not be correct or can only perform palliative surgery
• concommitant with mitral stenosis
• ischemic mitral regurgitation (for example, concommitant with anomalous origin of coronary artery)
• Barlow syndrome
• dysplasia of mitral leaflet
• complete/Partial endocardial cushion defect
• common atrioventricular valve
• atrioventricular common channel
• cardiomyopathy
• other mitral valve surgery contraindications

Children under the age of 14 with moderate to severe mitral valve regurgitation