Sinoatrial NodeHeart RateSinoatrial BlockHeartTachycardia, Sinoatrial Nodal ReentryBradycardiaHeart AtriaArrhythmia, SinusAtrioventricular NodeHeart BlockAutonomic Nervous SystemHeart Rate, FetalHeart FailureElectrocardiographyBiological ClocksHeart Conduction SystemBlood PressureAtrial FunctionRabbitsHeart DiseasesModels, CardiovascularAction PotentialsDogsHeart TransplantationHeart Defects, CongenitalHemodynamicsHeart ValvesMyocardial ContractionSympathetic Nervous SystemCardiac Pacing, ArtificialTachycardiaFetal HeartIsoproterenolParasympathetic Nervous SystemTime FactorsAdrenergic beta-AntagonistsHeart Function TestsAtropineSick Sinus SyndromeMyocytes, CardiacVagus NerveCardiotonic AgentsElectrocardiography, AmbulatoryTachycardia, SinusArrhythmias, CardiacAtrial Function, RightBaroreflexPhosphodiesterase 3 InhibitorsPropranololAdrenergic beta-AgonistsExercise TestElectrophysiologyPacemaker, ArtificialAdams-Stokes SyndromeAnti-Arrhythmia AgentsCalcium Channels, L-TypeMyocardiumOxygen ConsumptionPotassium ChannelsBenzazepinesTelemetryMembrane PotentialsAutonomic Nerve BlockCross CirculationGuinea PigsDose-Response Relationship, DrugConnexin 43Stroke VolumeRespirationDiastoleMyocardial IschemiaVentricular Function, LeftConnexinsCardiovascular Physiological PhenomenaPatch-Clamp TechniquesIon ChannelsEpinephrineReceptors, Adrenergic, betaPhysical ExertionCoronary DiseaseBundle of HisExerciseCardiovascular SystemRestCalcium Channels, T-TypePressoreceptorsPropanolaminesCardiac OutputCalciumHeart Arrest, InducedVenae CavaeParasympathetic Fibers, PostganglionicNorepinephrinePhosphodiesterase 4 InhibitorsSodium-Calcium ExchangerAcetylcholineMicroelectrodesCardiac MyosinsMyoblasts, CardiacTachycardia, Supraventricular