Relation Between Work and Labile Phosphate Content in the Isolated Dog Heart

Abstract

Starling heart-lung preparations of the dog (with only minor differences in heart rate) were subjected to changes in work load to study their effect on the amount of labile phosphate in the left ventricle. While increasing the work load three to fourfold by increasing output caused no change, doubling the work load by increasing the resistance was accompanied by a marked reduction in labile phosphate. The data suggest that the heart expends phosphate bond energy chiefly in overcoming resistance rather than in systolic emptying.