Cardiac toxicity due to anthracycline therapy is dose related, and congestive failure is a major limiting factor to therapy. Radionuclide cardiac evaluation provides a sensitive noninvasive method for detecting changes in cardiac function. Fifteen patients receiving either doxorubicin or daunomycin were evaluated with radionuclide ejection fractions (EFrn). The data indicate that the EFrn can detect an acute depressant cardiac action of these drugs as early as 24 hr after drug administration. In addition, a cumulative or chronic cardiac depression was noted; cumulative dosage of doxorubicin or daunomycin correlated with a reduced EFrn (p < 0.001). We conclude that (1) the EFrn can noninvasively detect significant changes in cardiac function at low cumulative doses of doxorubicin or daunomycin and (2) the EFrn may be useful in evaluating cardiac function in patients during doxorubicin or daunomycin therapy.