Twenty long-term survivors of childhood cancer underwent exercise echocardiography to evaluate possible late anthracycline-induced cardiac toxicity. Ten patients ages 10 to 20 years had received anthracyclines, and ten patients ages 8 to 27 years had not received anthracyclines as part of their medical regimen. Both groups had normal cardiac function at rest. Patients who had not received anthracyclines had a greater increase in M-mode shortening fraction (P less than 0.005), velocity of circumferential fiber shortening (P = 0.05), and Doppler aortic peak flow velocity (P = 0.01) than patients receiving anthracyclines. There were no significant differences in work performed, or increase in heart rate or blood pressure with exercise between the groups. These results suggest that subtle abnormalities in myocardial function exist which become apparent only after exercise in survivors of childhood cancer who have received anthracyclines and have normal resting cardiac function.