Heart RateElectrocardiographyHeartHeart Rate, FetalHeart FailureAutonomic Nervous SystemBlood PressureHeart DiseasesHeart TransplantationHeart Defects, CongenitalHemodynamicsFetal HeartSympathetic Nervous SystemElectrocardiography, AmbulatoryBaroreflexHeart AtriaAdrenergic beta-AntagonistsHeart ValvesExercise TestMyocardial ContractionHeart BlockMyocardiumTime FactorsOxygen ConsumptionHeart Function TestsParasympathetic Nervous SystemTelemetryDogsBradycardiaPropranolol