Changes in metabolite and high-energy phosphate levels in the non-infarcted portion of the left ventricle were studied in dogs from one to 10 days after coronary artery ligation. There was a marked fall in the adenosine triphosphate (ATP) levels in the non-infarcted region of the left ventricle 24 hr after infarction; a progressive rise occurred thereafter till the 10th day. Parallel changes were noted in the creatine-phosphate (CP) levels. The decrease in ATP and CP levels was not accompanied by significant changes in lactate or pyruvate content of the non-infarcted myocardium during the period of observation. When changes in high energy phosphates in non-infarcted myocardium were correlated with left ventricular function, a complex relationship was observed between the ATP content and the rate of left ventricular pressure rise (dp/dt) as well as stroke work. These results indicate that, after coronary artery ligation, significant changes occur in the high energy phosphate metabolism in the non-infarcted portion of the left ventricle and that a relationship may exist between these biochemical changes and left ventricular function.