Heart RateHeartHeart FailureHeart Rate, FetalBlood PressureAutonomic Nervous SystemHeart DiseasesHeart TransplantationHemodynamicsHeart Defects, CongenitalProton Pump InhibitorsFetal HeartTime FactorsSympathetic Nervous SystemElectrocardiography, AmbulatoryInfusion PumpsHeart AtriaBaroreflexElectrocardiographyAdrenergic beta-AntagonistsIon PumpsMyocardiumMyocardial ContractionHeart ValvesExercise TestDogsOxygen ConsumptionHeart BlockHeart Function TestsTelemetryRisk FactorsParasympathetic Nervous SystemBradycardiaPropranololStroke VolumeRespirationVentricular Function, LeftMyocardial IschemiaProspective StudiesExerciseCoronary DiseaseInfusion Pumps, ImplantableCardiovascular Physiological PhenomenaSodium-Potassium-Exchanging ATPasePhysical ExertionTachycardiaCardiac OutputCardiotonic AgentsRestAtropineCardiovascular SystemPressoreceptorsPropanolaminesReproducibility of ResultsHeart Arrest, InducedNorepinephrineDose-Response Relationship, DrugMyocardial InfarctionSinoatrial NodeModels, CardiovascularMyocytes, CardiacEchocardiographyTreatment OutcomeReflexCardiac Output, LowSignal Processing, Computer-AssistedFollow-Up StudiesReference ValuesPostureAutonomic Nervous System DiseasesOuabainRats, Sprague-DawleyDouble-Blind MethodArrhythmia, SinusCardiac Pacing, ArtificialIsoproterenolMetoprololSystoleAge FactorsSodiumRats, WistarPredictive Value of TestsSupine PositionRisk AssessmentEpinephrineCardiomyopathy, DilatedAlgorithmsBody TemperatureCohort StudiesRegression AnalysisRegional Blood FlowAnalysis of VarianceVentricular Dysfunction, LeftDiastoleUnited StatesModels, StatisticalPotassiumModels, BiologicalCircadian RhythmHeart, Artificial