Two groups of children with acute lymphoblastic leukemia or non-Hodgkin lymphoma, treated with anthracyclines (ANT), were studied: group I, consisting of 10 patients, with coenzyme Q10 (CoQ) therapy; group II, consisting of 10 patients without CoQ therapy. The ANT cumulative dose was 240 +/- 20.0 mg/m2 in group I and 252.0 +/- 20.1 mg/m2 in group II. Echocardiographic study was performed at the beginning, at the cumulative dose of 180 mg/m2 and at the end of therapy with ANT. Percentage left ventricular fractional shortening (%LVFS) decreased from baseline (40.36 +/- 4.6) to end value (35.82 +/- 5.02) (P < 0.05) in group I; %LVFS decreased from baseline (39.89 +/- 4.37) to end value (33.43 +/- 3.46) (P < 0.002) in group II. Interventricular septum wall thickening decreased only in group II from baseline (46.10 +/- 10.1) to end therapy (27.00 +/- 18.54) (P < 0.01). Septum wall motion abnormalities were detected only in 2 patients of group II. These data demonstrate a protective effect of CoQ on cardiac function during therapy with ANT.