Papillary MusclesMuscle NeoplasmsMusclesMyocardial ContractionMuscle ProteinsChordae TendineaeMuscle, SmoothMuscle, SkeletalMuscle ContractionMuscle Fibers, SkeletalMuscle, Smooth, VascularMitral Valve InsufficiencyGuinea PigsMuscle DevelopmentMitral ValveFerretsHeartAction PotentialsHeart VentriclesMyocardiumMuscle FatigueMuscle Fibers, Fast-TwitchMuscle DenervationIsometric ContractionMuscle Fibers, Slow-TwitchAequorinHeart Rupture, Post-InfarctionMyocytes, Smooth MuscleCalciumMuscle RelaxationMitochondria, MuscleRabbitsElectric StimulationPancreatic NeoplasmsCineradiographyNeck MusclesHeart RuptureOculomotor MusclesTime FactorsCatsMuscle, StriatedDogsNeoplasmsDepression, ChemicalMuscle SpindlesPurkinje FibersRespiratory MusclesIsoproterenolMuscle WeaknessVentricular FunctionMyofibrilsNeoplasms, Cystic, Mucinous, and SerousMitral Valve AnnuloplastyMembrane PotentialsEndocardiumAbdominal MusclesQuadriceps MuscleMuscle CellsElectrophysiologyCross CirculationRats, WistarBiomechanical PhenomenaMasseter MuscleCardiomyopathiesAnti-Arrhythmia AgentsFacial MusclesMasticatory MusclesStimulation, ChemicalIntercostal MusclesElectromyographyOuabainDose-Response Relationship, DrugHeart Conduction SystemMuscular AtrophyMicroelectrodesSkin NeoplasmsSatellite Cells, Skeletal MuscleRyanodineEchocardiographySarcolemmaSarcoplasmic ReticulumNeoplasms, Multiple PrimaryRupture, SpontaneousImmunohistochemistryCarnivoraPectoralis MusclesAdrenergic beta-AgonistsRefractory Period, ElectrophysiologicalCardiotonic AgentsMyosin Heavy ChainsEchocardiography, Three-DimensionalRats, Sprague-DawleyMuscular DiseasesMitral Valve ProlapseDigitoxinKidney NeoplasmsQuinidineCells, CulturedPerfusionEchocardiography, Transesophageal