Myocytes, CardiacMyocardiumCells, CulturedCell DifferentiationHeartAnimals, NewbornCardiomegalyMyocardial ContractionRats, Sprague-DawleyHeart VentriclesRats, WistarCalciumMitochondria, HeartMutationSignal TransductionMyocardial Reperfusion InjuryCardiotonic AgentsSarcomeresEmbryonic Stem CellsCell SizeMice, TransgenicApoptosisGATA4 Transcription FactorCalcium Channels, L-TypeIsoproterenolHypertrophyConnexin 43Muscle CellsMice, KnockoutMice, Inbred C57BLCalcium SignalingPhenotypeSarcoplasmic Reticulum Calcium-Transporting ATPasesSarcolemmaCardiac MyosinsMuscle ProteinsRNA, MessengerSodium-Calcium ExchangerCardiomyopathiesMyocardial IschemiaMyoblasts, Cardiac