Heart FailureVentricular FunctionElectrocardiographyHeart Conduction SystemLong QT SyndromeHeartHeart RateArrhythmias, CardiacAction PotentialsHeart VentriclesTorsades de PointesAnti-Arrhythmia AgentsMagnetocardiographyCardiac Pacing, ArtificialRefractory Period, ElectrophysiologicalSotalolDogsPericardiumPotassium Channels, Voltage-GatedKCNQ1 Potassium ChannelEther-A-Go-Go Potassium ChannelsBody Surface Potential MappingEndocardiumTachycardia, VentricularMexiletinePhenethylaminesDelayed Rectifier Potassium ChannelsPotassium ChannelsVentricular FibrillationElectrocardiography, AmbulatoryMyocytes, CardiacPotassium Channel BlockersMyocardiumVectorcardiographyElectrophysiologic Techniques, CardiacElectrophysiologyTime FactorsDeath, Sudden, CardiacCardiac Output, LowKv1.5 Potassium ChannelCardiac Complexes, PrematureVentricular Function, LeftHeart Failure, SystolicMyocardial ContractionPropanolaminesGuinea Pigs4-AminopyridineChromansHeart Failure, DiastolicPatch-Clamp TechniquesAtrial FibrillationMembrane PotentialsPredictive Value of TestsStroke VolumeHeart DiseasesExercise TestSulfonamidesCardiomyopathy, DilatedRabbitsVentricular Dysfunction, LeftHeart AtriaProspective StudiesAdrenergic beta-AntagonistsHeart TransplantationNatriuretic Peptide, BrainVentricular RemodelingHemodynamicsRisk FactorsDrug-Related Side Effects and Adverse ReactionsChronic DiseaseSodium ChannelsTreatment FailureRisk AssessmentLinear ModelsCardiotonic AgentsModels, CardiovascularReference ValuesEchocardiographyDose-Response Relationship, DrugRetrospective StudiesTreatment OutcomeDrug Evaluation, PreclinicalCardiomyopathiesHeart Defects, CongenitalFollow-Up StudiesMyocardial InfarctionCardiomegalyCase-Control StudiesPotassiumPrognosisCalciumVentricular DysfunctionDisease Models, AnimalSex FactorsMyocardial IschemiaHeart Function TestsBrugada SyndromePurkinje FibersDiureticsHeart Block