A Nomogram for Cardiac Contractility Involving Calcium, Potassium and Digitalis-Like Drugs

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Abstract
In nutrient media the frog (Rana pipiens) heart''s ventricle contracts maximally at a sharp concn. of K ions of 0.0048 M. Higher or lower concns. of K cause a reduction in contractility. The magnitude of the maximal contraction, however, is detd. by the concns. of Ca and of cardiac glycoside, e.g., digitoxin congener, which act synergistically. The traditional Ca:K ratio, therefore, is without direct mechanistic significance. A nomogram for cardiac contractility is presented which correlates the combined effects of K+, Ca++ and digitoxin congeners at 26[degree]C.