Atrial FunctionMuscle ContractionAtrial Function, LeftAtrial Premature ComplexesMyocardial ContractionHeart AtriaEchocardiography, Doppler, PulsedEchocardiography, DopplerMitral ValveFetal HeartBlood Flow VelocityIsometric ContractionDiastolePerinephritisPulmonary VeinsVentricular Function, LeftUterine ContractionAtrial FibrillationTricuspid ValveUltrasonography, PrenatalElectrocardiographyEchocardiographyUltrasonography, DopplerSystoleMitral Valve StenosisHeart RateBradycardiaMitral Valve InsufficiencyVena Cava, InferiorMuscle, SmoothDogsHeart Conduction SystemCardiac Pacing, ArtificialHeart VentriclesHeart Defects, CongenitalGestational AgeHeart Valve DiseasesPulmonary Wedge PressureHeartObservationCardiomegalyHemodynamicsPregnancyVentricular Dysfunction, LeftElectric StimulationStroke VolumeTime FactorsObserver VariationMuscle, SkeletalIsotonic ContractionVasoconstrictionCalciumGuinea PigsCardiac CatheterizationProspective StudiesMuscle, Smooth, VascularMuscle RelaxationMuscle FatigueBlood PressureChronic DiseaseElectromyographyPotassium ChlorideGastrointestinal MotilityTracheaVasoconstrictor AgentsPeristalsisUrinary BladderMusclesNorepinephrineDose-Response Relationship, DrugAcetylcholineRabbitsAtropineTreatment OutcomePhenylephrineVas DeferensIleumNifedipineAorta, ThoracicMuscle TonusCarbacholTorqueRats, Wistar15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic AcidMyosin Light Chainsrho-Associated KinasesRats, Sprague-DawleyMotor NeuronsSerotoninCaffeineMyometriumCalcium Channel BlockersMesenteric ArteriesMuscle Fibers, SkeletalMyosinsPotassiumVerapamilHistamineAdrenergic alpha-AgonistsMyography