AmrinoneMyocardial ContractionCardiotonic AgentsPapillary MusclesStimulation, ChemicalHeartMilrinoneBupranololAminopyridinesMyocardiumHeart AtriaGuinea PigsIsoproterenolHeart VentriclesThiadiazinesLycopusDepression, ChemicalDogsCalciumReserpineCardiac GlycosidesPhosphodiesterase InhibitorsOuabainVentricular FunctionAdrenergic beta-AgonistsAtrial FunctionDigitalis GlycosidesPyridonesStrophanthidinReceptors, Adrenergic, alphaHeart RatePyridazinesRewarmingPropranololPhenylephrineDiethylaminesReceptors, Adrenergic, betaFerretsDose-Response Relationship, DrugVerapamilAdrenergic beta-1 Receptor AgonistsTheophyllineAequorinAction PotentialsMyocytes, CardiacPhenylisopropyladenosineSodium-Calcium ExchangerAdrenergic beta-AntagonistsTyramineCyclic AMPPrazosinPhentolamine