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By following changes in arterial-coronary sinus plasma potassium concentration differences, the myocardial potassium balance was studied during the increased heart rate produced by cardioaccelerator nerve or right atrial stimulation. With cardioaccelerator nerve stimulation there was an initial loss of myocardial potassium of brief duration, followed by an uptake for the duration of the stimulation. Atrial stimulation leads predominantly to a loss of myocardial potassium, particularly when the reflex effects of marked cardiac acceleration were minimized by cardioaccelerator nerve excision and support of venous return by abdominal binding. It is suggested that the chronotropic action of cardiac sympathetic nerves tends to cause a loss of potassium, but that this is normally circumvented by some other action of the nerves in promoting potassium uptake.

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