The relation of potassium to digitalis effectiveness and toxicity.

The concentration of potassium in the extracellular fluid, and presumably in the cell membrane and intracellular contents of the myocardial fibre, has a significant influence on the contractibility, irritability, conduction and rhythmic tendency of the heart muscle. The therapeutic and toxic dosage of digitalis is clinically affected by the variations in potassium concentrations. The range between therapeutic and toxic dosages of digitalis and sensitivity to bodily potassium depletion varies with the degree of failure of the myocardium and passive congestion of the liver.