Heart RateExercise TestHeartHeart Defects, CongenitalFetal HeartMyocardiumHeart Rate, FetalHeart FailureAutonomic Nervous SystemBlood PressureHeart DiseasesHeart TransplantationHemodynamicsSympathetic Nervous SystemElectrocardiography, AmbulatoryBaroreflexHeart AtriaElectrocardiographyAdrenergic beta-AntagonistsHeart ValvesMyocardial ContractionHeart BlockTime FactorsOxygen ConsumptionHeart Function TestsParasympathetic Nervous SystemTelemetryDogsBradycardiaPropranololStroke VolumeRespirationMyocardial IschemiaVentricular Function, LeftCardiovascular Physiological PhenomenaTachycardiaPhysical ExertionCoronary DiseaseExerciseCardiovascular SystemAtropineRestPressoreceptorsPropanolaminesCardiac OutputCardiotonic AgentsHeart Arrest, InducedNorepinephrineSinoatrial Node