Heart RateHeartHeart Rate, FetalHeart FailureAutonomic Nervous SystemBlood PressureHeart DiseasesHeart TransplantationHeart Defects, CongenitalHemodynamicsFetal HeartTime FactorsSympathetic Nervous SystemElectrocardiography, AmbulatoryBaroreflexHeart AtriaElectrocardiographyAdrenergic beta-AntagonistsHeart ValvesExercise TestMyocardial ContractionMyocardiumHeart BlockOxygen ConsumptionDogsHeart Function TestsTelemetryParasympathetic Nervous SystemRisk FactorsBradycardiaPropranololRespirationStroke VolumeMyocardial IschemiaVentricular Function, LeftCoronary DiseaseExerciseCardiovascular Physiological PhenomenaPhysical ExertionProspective StudiesTachycardiaRestCardiac OutputCardiovascular SystemAtropinePropanolaminesPressoreceptorsCardiotonic AgentsHeart Arrest, InducedReproducibility of ResultsNorepinephrineSinoatrial NodeMyocardial InfarctionEchocardiographyReflexSignal Processing, Computer-AssistedAutonomic Nervous System DiseasesModels, CardiovascularDose-Response Relationship, DrugPostureMyocytes, CardiacFollow-Up StudiesCardiac Output, LowArrhythmia, SinusReference ValuesCardiac Pacing, ArtificialDouble-Blind MethodMetoprololSupine PositionIsoproterenolTreatment OutcomeAge FactorsSystolePredictive Value of TestsRisk AssessmentBody TemperatureRats, Sprague-DawleyRegression AnalysisEpinephrineCohort StudiesCardiomyopathy, DilatedModels, StatisticalAlgorithmsUnited StatesDiastoleAnalysis of VarianceRegional Blood FlowVentricular Dysfunction, LeftRats, WistarCircadian RhythmPrevalenceLinear ModelsArrhythmias, CardiacTilt-Table TestFetal MonitoringHypotensionInfant, NewbornAnti-Arrhythmia AgentsCardiomegalyAtenolol