The vagus and the ventricles.
D000200:Action Potentials; D000818:Animals; D002036:Bundle of His / Q000502:physiology; D002799:Cholinergic Fibers / Q000502:physiology; D004285:Dogs; D004558:Electric Stimulation; D006329:Heart Conduction System / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D010656:Phenylephrine / Q000494:pharmacology; D011690:Purkinje Fibers / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology; D014630:Vagus Nerve / Q000502:physiology*; D016276:Ventricular Function
D011976:Receptors, Muscarinic; D010656:Phenylephrine