Pacemaker, ArtificialHeartHeart RateBiological ClocksHeart BlockSinoatrial NodeSick Sinus SyndromeHeart FailureEquipment FailureHeart DiseasesAtrioventricular BlockBradycardiaHeart Defects, CongenitalHeart TransplantationHeart AtriaHyperpolarization-Activated Cyclic Nucleotide-Gated ChannelsFetal HeartCircadian RhythmHeart ValvesElectrodes, ImplantedInterstitial Cells of CajalSuprachiasmatic NucleusDevice RemovalTime FactorsAction PotentialsAtrioventricular NodeEquipment SafetyMyocardiumArrhythmias, CardiacHeart Conduction SystemCyclic Nucleotide-Gated Cation ChannelsPeriodicityElectrocardiographyMyocardial ContractionMyocytes, CardiacHeart InjuriesDefibrillators, ImplantableArrhythmia, SinusHeart Function TestsTachycardiaAtrial FibrillationAtrial FunctionElectrophysiologyTreatment OutcomeHeart Arrest, InducedSyncopeEquipment DesignDogsFlufenamic AcidFollow-Up StudiesMembrane PotentialsHemodynamicsPeriod Circadian ProteinsHeart Valve ProsthesisMyocardial IschemiaEchocardiographyProspective StudiesHeart ArrestHeart SeptumElectrocardiography, AmbulatoryProsthesis ImplantationPotassium ChannelsForeign-Body MigrationCardiac Output, LowStroke VolumeIon ChannelsVentricular Function, LeftCalciumCoronary DiseaseCardiotonic AgentsVentricular Dysfunction, LeftCardiomyopathiesRabbitsTelemetryRisk FactorsIsoproterenolPerfusionCardiomyopathy, DilatedMyocardial InfarctionAnti-Arrhythmia AgentsRheumatic Heart DiseaseRespiratory CenterElectric Power SuppliesHeart Valve Prosthesis ImplantationPatch-Clamp TechniquesPurkinje FibersSinoatrial BlockNeuronsElectromagnetic PhenomenaRetrospective StudiesAdrenergic beta-AntagonistsExercise TestHeart, ArtificialHeart Failure, SystolicCardiomegalyAutonomic Nervous SystemBundle of HisPotassiumElectric StimulationElectrophysiologic Techniques, Cardiac