Arrhythmias, CardiacPacemaker, ArtificialArrhythmia, SinusMyocytes, CardiacElectrocardiographySinoatrial NodeBiological ClocksHeartHeart BlockSick Sinus SyndromeDeath, Sudden, CardiacHeart Conduction SystemBradycardiaCardiac OutputTachycardia, VentricularAnti-Arrhythmia AgentsAtrioventricular BlockHeart RateCardiac Surgical ProceduresVentricular FibrillationHeart VentriclesEquipment FailureTachycardiaCardiac Pacing, ArtificialDefibrillators, ImplantableAtrial FibrillationMyocardiumElectrocardiography, AmbulatoryVentricular Premature ComplexesAction PotentialsHeart AtriaTime FactorsHeart DiseasesDogsMyocardial ContractionElectrophysiologic Techniques, CardiacHyperpolarization-Activated Cyclic Nucleotide-Gated ChannelsHeart ArrestLong QT SyndromeElectrophysiologyHeart FailureCardiac Complexes, PrematureCardiomyopathiesCardiac CatheterizationTreatment OutcomeCatheter AblationCardiomegalyEchocardiographyTachycardia, SupraventricularCircadian RhythmMyocardial InfarctionSyncopeCardiac TamponadeVentricular DysfunctionAtrioventricular NodeElectric CountershockCardiac ElectrophysiologyElectrodes, ImplantedAtrial FlutterFollow-Up StudiesMyocardial IschemiaHemodynamicsProspective StudiesNAV1.5 Voltage-Gated Sodium ChannelModels, CardiovascularDevice RemovalAtrial FunctionInterstitial Cells of CajalVentricular FunctionMyoblasts, CardiacCalciumEquipment SafetyVentricular Function, LeftPericardiumSuprachiasmatic NucleusTelemetryHeart Defects, CongenitalStroke VolumePotassium ChannelsPurkinje FibersMembrane PotentialsHeart InjuriesAmiodaroneCardiomyopathy, DilatedTorsades de PointesCyclic Nucleotide-Gated Cation ChannelsVentricular Dysfunction, LeftCardiac Output, LowCardiotonic AgentsRetrospective StudiesEquipment DesignBlood PressureCardiac Imaging TechniquesFlecainidePeriodicityIsoproterenolMyocardial Reperfusion InjuryRisk FactorsSodium ChannelsHeart Transplantation