Myocytes, CardiacMyocardiumCells, CulturedCell DifferentiationHeartAnimals, NewbornCardiomegalyMyocardial ContractionRats, Sprague-DawleyHeart VentriclesRats, WistarCalciumMitochondria, HeartMyocardial Reperfusion InjuryCardiotonic AgentsSarcomeresEmbryonic Stem CellsCell SizeGATA4 Transcription FactorSignal TransductionCalcium Channels, L-TypeIsoproterenolApoptosisHypertrophyConnexin 43Muscle CellsMice, TransgenicCalcium SignalingSarcoplasmic Reticulum Calcium-Transporting ATPasesSarcolemmaCardiac Myosins