Two cases of anthracycline-induced congestive heart failure are described. Serial assessment of cardiac function during treatment showed early deterioration of the systolic time intervals of the left ventricle (LSTI) before congestive cardiomyopathy could be demonstrated by echocardiography. We recommend that the cardiac function should be assessed regularly during anthracycline therapy by systolic time intervals and echocardiography to reveal early signs of cardiotoxic effect and that anthracycline therapy should be stopped when LSTI is 0.45 or when it has increased more than 50% compared to pretreatment values.