Pacemaker, ArtificialHeart VentriclesCerebral VentriclesBiological ClocksSinoatrial NodeThird VentricleFourth VentricleSick Sinus SyndromeHeart BlockLateral VentriclesCerebral Ventricle NeoplasmsEquipment FailureAtrioventricular BlockBradycardiaVentricular FunctionHyperpolarization-Activated Cyclic Nucleotide-Gated ChannelsHeartElectrocardiographyHeart Conduction SystemHeart AtriaElectrodes, ImplantedMyocardiumArrhythmias, CardiacCircadian RhythmDevice RemovalInterstitial Cells of CajalAction PotentialsSuprachiasmatic NucleusMyocardial ContractionDogsAtrioventricular NodeEquipment SafetyAtrial FunctionElectrophysiologyHeart RatePeriodicityVentricular Function, RightCyclic Nucleotide-Gated Cation ChannelsEchocardiographyTime FactorsHeart Defects, CongenitalDefibrillators, ImplantableEndocardiumForeign-Body MigrationPericardiumTachycardiaVentricular Function, LeftDouble Outlet Right VentricleEquipment DesignMembrane PotentialsHeart InjuriesHydrocephalusFlufenamic AcidArrhythmia, SinusSyncopeHeart SeptumAtrial FibrillationVentricular Dysfunction, RightTransposition of Great VesselsPeriod Circadian ProteinsProsthesis ImplantationTreatment OutcomePotassium ChannelsMyocytes, CardiacCerebral VentriculographyStroke VolumeInjections, IntraventricularVentricular Dysfunction, LeftHeart FailureHemodynamicsTricuspid ValvePurkinje FibersIon ChannelsDiastoleNeuronsEpendymaVentricular SeptumHeart Septal Defects, VentricularElectrophysiologic Techniques, CardiacFollow-Up StudiesPatch-Clamp TechniquesCardiac Surgical ProceduresRabbitsBundle of HisCardiac CatheterizationCalciumBundle-Branch BlockCardiomyopathiesMagnetic Resonance ImagingRespiratory CenterVentricular DysfunctionElectric Power SuppliesIsoproterenolHypertrophy, Right VentricularHeart DiseasesSinoatrial BlockPotassiumTricuspid Valve StenosisElectric StimulationAnti-Arrhythmia Agents