Effect and Safety of Flecainide and Metoprolol Versus Metoprolol Alone to Suppress Ventricular Arrhythmias in Arrhythmic Mitral Valve Prolapse

Inclusion Criteria: * Participants must be 18 years of age or older at the time of signing the informed consent. * Participants must have mitral valve prolapse evident by echocardiography or cardiac magnetic resonance imaging, defined as more than or equal to 2 mm atrial displacement of any part of the mitral leaflets. * Participants must have ventricular arrhythmias, defined as at least one of the following (i) premature ventricular complex burden ≥3% per 24 hours by Holter monitoring, (ii) premature ventricular complex burden ≥1% per 24 hours if multifocal or occurring in bi-/trigemini and/or couplets by Holter monitoring, (iii) sustained or non-sustained ventricular tachycardia, (iv) aborted cardiac arrest. * Participants must have a clinical indication for antiarrhythmic treatment due to ventricular arrhythmias. * Participants must be capable of giving signed informed consent, which includes compliance with the requirements and restrictions listed in the informed consent form (ICF). * Participants (only women of childbearing) must accede to mandatory use of a contraceptive method for the duration of the trial and until 3 days after discontinuation of study medication. Exclusion Criteria: * Strict contraindications to flecainide or metoprolol use * Heart failure (signs or symptoms, elevated N-terminal proBNP) * Abnormal liver or kidney function (Aspartate aminotransferase (AST)/Alanine aminotransferase (ALT) three times upper normal, estimated glomerular filtration (eGRF) \<60) * Prior myocardial infarction or ischemic heart disease * Ion channelopathy, including Brugada syndrome and long QT syndrome * Genetic cardiomyopathy (hypertrophic cardiomyopathy, arrhythmogenic cardiomyopathy, dilated cardiomyopathy, including genotype positive phenotype negative individuals) * Atrial flutter or permanent atrial fibrillation * Sinus node dysfunction * Ongoing electrolyte disorders * More than moderate valvular disease according to international guidelines * Pre-excitation * Any degree of AV-block, except due to enhanced vagal tone (e.g. Wenckebach-block at night in young athletes or 1st-degree AV block that disappears during exercise) * Bundle branch block (QRS duration \>120 ms) or intraventricular conduction defect with QRS \>120 ms. * Prior flecainide therapy. * Concomitant use of the following medications (i) CYP2D6 inhibitors/inducers, (ii) class I, III or IV antiarrhythmic drugs, (iii) clozapine, quinidine, cimetidine, bupropion, or (iii) monoamineoxidase (MAO) inhibitors * Pregnancy * Not willing to use a mandatory contraceptive method for the duration of the trial.