Tachycardia, Ectopic JunctionalTachycardia, SupraventricularTachycardiaTachycardia, Ectopic AtrialTachycardia, VentricularTachycardia, ParoxysmalPropafenoneElectrocardiographyTachycardia, Atrioventricular Nodal ReentryAnti-Arrhythmia AgentsAmiodaroneTachycardia, SinusCatheter AblationAtrioventricular NodeHeart Conduction SystemWolff-Parkinson-White SyndromeElectrophysiologic Techniques, CardiacArrhythmias, CardiacCardiac Pacing, ArtificialTachycardia, Sinoatrial Nodal ReentryBundle of HisPostural Orthostatic Tachycardia SyndromeInfant, NewbornTachycardia, ReciprocatingFlecainideAtrial Premature ComplexesAtrial FlutterHydrops FetalisElectrocardiography, AmbulatoryHeart RateBody Surface Potential MappingCardiac Complexes, PrematurePre-Excitation SyndromesVentricular FibrillationAccessory Atrioventricular BundleDigoxinDefibrillators, ImplantableAtrial FibrillationHeart AtriaVentricular Premature ComplexesHeart BlockFetal DiseasesElectric CountershockProcainamideSotalolTreatment OutcomeFollow-Up StudiesSyncopeHeart VentriclesElectrocoagulationElectrophysiologyBundle-Branch BlockAtrioventricular BlockCryosurgeryDeath, Sudden, CardiacVerapamilRecurrenceEndocardiumBradycardiaPacemaker, ArtificialSinoatrial NodeTime FactorsHeart Rate, FetalCardiomyopathiesRetrospective StudiesDogsEchocardiographyAdrenergic beta-AntagonistsEpicardial MappingHeartDisopyramideCardiomyopathy, DilatedHeart Defects, CongenitalHemodynamicsProspective Studies