Pacemaker, ArtificialSinoatrial NodeAdams-Stokes SyndromeHyperpolarization-Activated Cyclic Nucleotide-Gated ChannelsBiological ClocksBradycardiaEquipment FailureHeart BlockSick Sinus SyndromeEquipment SafetyArrhythmia, SinusMyocytes, CardiacCyclic Nucleotide-Gated Cation ChannelsInsurance, AccidentHeart RateHeart Conduction SystemHeartCardiac Pacing, ArtificialElectrodes, ImplantedElectromagnetic FieldsHeart ArrestElectrocardiographyIon ChannelsEquipment DesignHeart AtriaPeriodicityArrhythmias, CardiacCardiac OutputAction PotentialsPotassium ChannelsMyocardial ContractionSodium-Calcium ExchangerElectrophysiologyRabbitsCardiac Surgical ProceduresMembrane PotentialsAtrioventricular BlockReceptors, Adrenergic, betaDeath, Sudden, CardiacCalciumHeart DiseasesHeart VentriclesCardiac TamponadeCardiac CatheterizationCircadian RhythmMyocardiumTime FactorsCardiomegalyInterstitial Cells of CajalDevice RemovalHeart FailureSuprachiasmatic NucleusMyoblasts, CardiacDefibrillators, ImplantableEchocardiographyCardiomyopathiesTreatment OutcomeAtrioventricular NodeDogsHeart InjuriesHemodynamicsCardiac Output, LowSyncopeCardiac ElectrophysiologyAtrial FibrillationCardiac MyosinsTachycardiaCardiac Resynchronization TherapyCardiac Imaging TechniquesAtrial FunctionHeart TransplantationProspective StudiesCardiac GlycosidesFollow-Up StudiesVentricular Function, LeftHeart Defects, CongenitalMyocardial InfarctionStroke VolumeFlufenamic AcidVentricular FunctionOut-of-Hospital Cardiac ArrestVentricular Dysfunction, LeftTroponin ICardiac VolumePurkinje FibersPeriod Circadian ProteinsVentricular RemodelingProsthesis ImplantationCardiotonic AgentsIsoproterenolHeart Function TestsCardiac Care FacilitiesPatch-Clamp TechniquesForeign-Body MigrationRetrospective StudiesBlood PressureElectrophysiologic Techniques, CardiacElectrocardiography, AmbulatoryCells, CulturedCardiomyopathy, Dilated