In patients with iron overload associated with severe, transfusion-dependent beta-thalassemia, congestive heart failure develops during the second decade of life. Biventricular heart function was studied by multigated radionuclide angiography in 22 patients with beta-thalassemia major. Six patients were symptomatic. Congestive heart failure developed in five patients at the time of blood transfusions, and one other patient had been treated for multiple ventricular extrasystole. The mean (+/- SD) left ventricular ejection fraction was normal (63.0% +/- 7.6%). Only one patient had a left ventricular ejection fraction under the normal level (less than 50%). The mean (+/- SD) right ventricular fraction (RVEF) was 33.3% +/- 9.4%. In only three patients was the RVEF normal (greater than or equal to 40%); an RVEF under 30% was registered in six patients. We suggest that the early right ventricular dysfunction in patients with beta-thalassemia may be due to pulmonary hypertension secondary to iron overload and iron deposits in the ventricles.