MilrinonePyridonesPhosphodiesterase 3 InhibitorsPhosphodiesterase InhibitorsAmrinoneCardiotonic AgentsMyocytes, CardiacCyclic Nucleotide Phosphodiesterases, Type 3Cardiac OutputHeartCardiac Surgical ProceduresArrhythmias, CardiacHydrazones3',5'-Cyclic-AMP PhosphodiesterasesPyridazinesMyocardial ContractionDeath, Sudden, CardiacMyocardiumHemodynamicsHeart FailureVasodilator AgentsAdrenergic beta-1 Receptor Antagonists