Polychemotherapy including idarubicin was administered during the second trimester to treat acute lymphoblastic leukemia. The infant delivered at 28 weeks' gestation had acute cardiac failure attributed to the cardiotoxic effect of idarubicin. Cardiotoxicity may be caused by idarubicin's biophysical properties that facilitate its transplacental passage. Idarubicin should be used with extreme caution during pregnancy.