Anthracyclines have greatly contributed to improvement in the prognosis of certain cancers, but their beneficial effect is impaired by an unquestionable toxicity affecting notably the heart. Changes in blood pressure or electrocardiograms, benign pericardial reactions and rare but severe myocarditis may occur at an early stage of treatment. The cumulative toxicity of anthracyclines limits their use. With a cumulative dose of 550 mg/m2 the mean incidence of toxicity varies from 5 to 10 percent. The occurrence of toxicity largely depends on the total dose, but other factors such as patient's age and general condition, and previous treatments with chemo- or radiotherapy must be taken into account. The best methods to monitor the cardiotoxicity of anthracyclines are echocardiography, radionuclide study of ejection fraction and myocardial biopsy for histological study. The rational use of these three types of examination must be adjusted to each individual patient. It should reduce the incidence of severe myocarditis which sometimes cancels all the beneficial effects of the anticancer treatment.