The effects of fructose-1,6-diphosphate (FDP) on cardiac activity were studied in 20 patients with chronic ischemic heart disease. Each patient received intravenously, in two different days, a single dose of FDP 20 g and placebo, according to a cross-over study design. Immediately prior to and ten minutes following each dosing, patients underwent an echocardiographic assessment. The comparison of pre- and post-treatment readings indicates that the diasto-systolic difference of left ventricular dimension increased by 10% after FDP (p less than 0.01). Similarly the increment of interventricular septum thickness increased by 16% (p less than 0.01) and that of posterior left ventricular wall thickness by 19% (p less than 0.01). In contrast the changes recorded after placebo treatment were far from being significant. These data indicate that the acute administration of a single dose of FDP may improve the cardiac performance in patients with chronic ischemic heart disease.