The effects of adriamycin and daunomycin on cardiac function were studied in 33 patients with acute leukemia (16 cases), neuroblastoma (5 cases), osteosarcoma (4 cases), malignant lymphoma (3 cases), rhabdomyosarcoma (3 cases) and malignant histiocytosis (2 cases). The left ventricular function was evaluated by serial echocardiographic assessment. Ejection fraction (E.F.) and shortening fraction (S.F.) of left ventricule were calculated from echocardiographic measurements. Seven of 33 cases (21.2%) revealed the decrease of E.F. and S.F. There was the significant correlation between total doses of daunomycin and E.F. Three patients died of severe congestive heart failure probably due to daunomycin administration. Usually, cardiac dysfunction caused by these drugs has improved within 3 months after the discontinuation.