The goal of this observational study is to compare the safety and effectiveness of a modified drug therapy with traditional drug therapy in pediatric patients with mild to moderate mitral valve regurgitation.

The main questions it aims to answer are:

• Can a modified drug therapy improve both left ventricular and mitral valve function in pediatric patients with mild to moderate mitral valve regurgitation?
• Can the adverse drug reactions caused by the modified drug therapy be non-inferior (clinically acceptable) to those of the traditional drug therapy? Participants will be assigned to either the Modified Drug Therapy Group (comprising angiotensin-converting enzyme inhibitor (ACE-I), beta-blockers, diuretics, potassium supplements, and spironolactone) or the Traditional Drug Therapy Group (diuretics and potassium supplements) based on personal preferences and clinical assessments by their attending physicians. They will undergo a one-year course of medication. Additionally, echocardiography, electrocardiograms, complete blood counts, biochemical tests, and measurements of N-terminal pro-brain natriuretic peptide (NT-proBNP) were conducted before the initiation of medication therapy and at 3 months, 6 months, and 12 months after treatment commencement.

Researchers will compare the Modified Drug Therapy Group and the Traditional Drug Therapy Group to see if the recurrence rate of moderate to severe mitral valve regurgitation, as assessed by echocardiography after 12 months of treatment, 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
• moderate to severe mitral regurgitation requires mitral valve surgery

Children under the age of 14 with moderate to severe mitral valve regurgitation, without contraindications for mitral valve repair, and without an immediate need for surgery.