Atrioventricular NodeAtrial FibrillationHeart BlockParasympathectomyRefractory Period, ElectrophysiologicalCardiac Pacing, ArtificialAnti-Arrhythmia AgentsAtrial FlutterMagnetocardiographyHeart RateAmiodaroneCatheter AblationCervical PlexusPacemaker, ArtificialElectrocardiographyTachycardiaHeart VentriclesTachycardia, SupraventricularHeart Conduction SystemDiltiazemPropafenoneHeart AtriaTachycardia, ParoxysmalDogsBradycardiaElectric CountershockAtrial FunctionMetoprololVentricular DysfunctionVentricular FunctionParasympatholyticsTachycardia, Atrioventricular Nodal ReentryVagus NerveWolff-Parkinson-White SyndromeFetal DiseasesElectrocardiography, AmbulatoryCardiac OutputAdrenergic beta-AntagonistsArrhythmias, CardiacAtropineTreatment OutcomeElectric StimulationRestUltrasonographyElectrophysiologyFollow-Up StudiesRabbitsTime FactorsProspective Studies