on the inotropic effects of nueleosides on acute ventricular failure in the isolated dog heart, 1 we have investigated myocardial purine and pyrimidine derivatives, including nucleotide components, in similar types of cardiac failure. Although other workers have examined high-energy phosphate compounds in cardiac failure, no total pattern studies have been made, and the reported findings relative to adenine nucleotides are inconsistent. 2 " 5 "With the recent development of analytical techniques allowing reliable quantitative separation and measure of tissue nucleotides 6 and their derivatives, it has become possible to establish definitively their distribution in myocardium.The experimental preparation chosen provided both a failing and a nonfailing ventricle in a single heart, permitting the unique advantage of the use of one ventricle as a biochemical control for the other. We had previously shown that unilateral left ventricular failure could be produced without involving the right ventricle, 7 by a heniodynamic stress rather than the use of drugs, which complicated the results of other workers. 8 ' 9 The type of failure induced in the present experiments is defined as ventricular insufficiency or inadequacy of response to increased work loads, resulting from (1) acute and (2) chronic heniodynamic overloading of the left ventricle.