Heart RateHeartHeart Rate, FetalHeart FailureBlood PressureAutonomic Nervous SystemHeart DiseasesHeart TransplantationHemodynamicsHeart Defects, CongenitalTime FactorsFetal HeartSympathetic Nervous SystemElectrocardiography, AmbulatoryBaroreflexHeart AtriaElectrocardiographyAdrenergic beta-AntagonistsExercise TestMyocardial ContractionMyocardiumOxygen ConsumptionHeart ValvesDogsHeart BlockHeart Function TestsTelemetryRisk FactorsParasympathetic Nervous SystemRespirationBradycardiaPropranololStroke VolumePhysical ExertionExerciseProspective StudiesMyocardial IschemiaVentricular Function, LeftDose-Response Relationship, DrugCoronary DiseaseReproducibility of ResultsCardiovascular Physiological PhenomenaTachycardiaCardiac OutputAtropineRestCardiovascular SystemPropanolaminesCardiotonic AgentsNorepinephrinePressoreceptorsHeart Arrest, InducedSinoatrial NodeMyocardial InfarctionReference ValuesTreatment OutcomeFollow-Up StudiesEchocardiographySignal Processing, Computer-AssistedAlgorithmsModels, CardiovascularReflexDouble-Blind MethodPostureAutonomic Nervous System DiseasesMyocytes, CardiacModels, StatisticalCardiac Output, LowIsoproterenolAge FactorsArrhythmia, SinusRats, Sprague-DawleyPredictive Value of TestsCardiac Pacing, ArtificialAnalysis of VarianceRegression AnalysisMetoprololBody TemperatureSupine PositionRats, WistarSystoleRisk AssessmentCohort StudiesEpinephrineRegional Blood FlowModels, BiologicalComputer SimulationUnited StatesLinear ModelsDiastoleCardiomyopathy, DilatedCircadian RhythmSensitivity and SpecificityLikelihood FunctionsBody WeightVentricular Dysfunction, LeftCross-Over StudiesOxygenPrevalenceInfant, Newborn