TachycardiaTachycardia, VentricularTachycardia, SupraventricularHeartTachycardia, Atrioventricular Nodal ReentryTachycardia, ParoxysmalTachycardia, Ectopic AtrialTachycardia, SinusHeart RateCatheter AblationElectrocardiographyTachycardia, Ectopic JunctionalPostural Orthostatic Tachycardia SyndromeTachycardia, ReciprocatingTachycardia, Sinoatrial Nodal ReentryCardiac Pacing, ArtificialElectrophysiologic Techniques, CardiacHeart Conduction SystemAnti-Arrhythmia AgentsAtrioventricular NodeHeart FailureHeart AtriaBundle of HisBody Surface Potential MappingHeart DiseasesHeart BlockHeart Defects, CongenitalVentricular FibrillationArrhythmias, CardiacWolff-Parkinson-White SyndromeHeart TransplantationElectrocardiography, AmbulatoryDefibrillators, ImplantableAmiodaroneEndocardiumFetal HeartVentricular Premature ComplexesFlecainideCryosurgeryFollow-Up StudiesProcainamideTreatment OutcomeCardiac Complexes, PrematureDeath, Sudden, CardiacCardiomyopathiesAtrial FlutterHeart ValvesPre-Excitation SyndromesBundle-Branch BlockHemodynamicsTime FactorsMyocardiumDogsAccessory Atrioventricular BundleHeart VentriclesElectric CountershockSyncopeAdrenergic beta-AntagonistsElectrophysiologyEpicardial MappingMyocardial InfarctionAtrial FibrillationCardiomyopathy, DilatedMyocardial IschemiaEchocardiographyMyocardial ContractionSotalolHeart ArrestHeart Function TestsPacemaker, ArtificialRecurrenceHydrops FetalisProspective StudiesMyocytes, CardiacArrhythmogenic Right Ventricular DysplasiaStroke VolumeCoronary DiseasePropranololHeart SeptumRetrospective StudiesVentricular Dysfunction, LeftIsoproterenolVentricular DysfunctionCardiac ElectrophysiologySinoatrial NodeVentricular Function, LeftSympathetic Nervous SystemDigoxinCardiac CatheterizationVerapamilAutonomic Nervous SystemPropafenoneHeart Rate, FetalHeart Arrest, InducedAtrioventricular BlockPericardiumCardiotonic AgentsPropanolaminesBradycardiaCardiac Output, Low