Myocytes, CardiacHeartMyocardiumCells, CulturedCardiomegalyCardiac OutputMyocardial ContractionArrhythmias, CardiacHeart VentriclesAnimals, NewbornCardiac Surgical ProceduresRats, Sprague-DawleyDeath, Sudden, CardiacRats, WistarCalciumHeart DiseasesTime FactorsMyoblasts, CardiacCardiomyopathiesCardiac MyosinsHeart FailureCardiotonic AgentsCell DifferentiationMitochondria, HeartCardiac Pacing, ArtificialSignal TransductionVentricular RemodelingSarcomeresMyocardial Reperfusion InjuryMyocardial InfarctionCardiac TamponadeApoptosisMyocardial IschemiaMice, TransgenicIsoproterenolDisease Models, AnimalGATA4 Transcription FactorEmbryonic Stem CellsCardiac CatheterizationCardiomyopathy, DilatedCell SizeMice, Inbred C57BLTroponin IRNA, MessengerCalcium Channels, L-TypeModels, BiologicalEchocardiographyHeart ArrestCell LineMuscle CellsModels, CardiovascularMuscle ProteinsSarcolemmaCell Culture TechniquesDose-Response Relationship, DrugSarcoplasmic Reticulum Calcium-Transporting ATPasesGene Expression RegulationVentricular Function, LeftCell SurvivalHeart AtriaAtrial Natriuretic FactorFibrosisElectrocardiographyHemodynamicsHypertrophyHeart RateCalcium SignalingMice, KnockoutCoculture TechniquesConnexin 43Gene ExpressionDogsSodium-Calcium ExchangerAdrenergic beta-AgonistsBlotting, WesternVentricular MyosinsCardiac Output, LowReverse Transcriptase Polymerase Chain ReactionMicroscopy, ConfocalPhosphorylationAction PotentialsCardiac Imaging TechniquesHeart TransplantationTroponin TReactive Oxygen SpeciesFetal HeartHeart InjuriesVentricular FunctionCell HypoxiaModels, AnimalCardiac GlycosidesHeart Conduction SystemCardiac VolumeHeart Function TestsStem CellsImmunohistochemistryPatch-Clamp TechniquesFibroblastsOxidative StressMyofibrils