The Relationship between Myocardial Content of Digoxin and Increase in Myocardial Contractility

The effect of digoxin on the contractility of the nonfailing heart was studied in anaesthetized dogs receiving continuous infusion of digoxin 0.8 jig/kg/ min. The contractility, described by Vce5was increased to 30 % above control levels after infusion of 35 μg/kg of digoxin. From this point only an insignificant increase in contractility was obtained following futher infusion of digoxin. The myocardial content of digoxin, measured by a radio immuno method, was proportional to the cummulated dose and calculated to be about 140 ng/g tissue, when the maximal increase in contractility was achieved. The content of digoxin in the myocardium of 275 ng/g tissue was not associated with dysrhythmias.