Study of Innovative Drug Strategies in Improving Left Ventricular Function After Mitral Repair

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 after mitral repair. The main questions it aims to answer are: * Can a modified drug therapy improve both left ventricular and mitral valve function in pediatric patients after mitral repair? * 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 6-months 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 1 month, 3 months, and 6 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 6 months of treatment, is lower in the former than in the latter.