Excitation Contraction CouplingArrhythmias, CardiacMuscle ContractionMyocytes, CardiacArrhythmia, SinusIsometric ContractionMyocardial ContractionHeartElectrocardiographyDeath, Sudden, CardiacUterine ContractionCardiac OutputTachycardia, VentricularElectric StimulationAction PotentialsCalciumAnti-Arrhythmia AgentsHeart VentriclesMyocardiumTime FactorsHeart Conduction SystemVentricular FibrillationCardiac Pacing, ArtificialHeart RateMuscle, SmoothCardiac Surgical ProceduresDogsVentricular Premature Complexes