The effect of iron overload on left ventricular (LV) performance was studied in 60 patients with beta-thalassemia. Patients were divided into 3 groups according to the number of blood units (BU) received. Clinically, 14 patients were in advanced classes (III and IV) of congestive heart failure (CHF). LV performance was extensively studied by M-mode echocardiography, and the results were correlated to BU transfused and CHF presence. E point-septal separation, LV systolic and diastolic dimensions had greater values in CHF patients (p less than 0.0001). The percentage shortening of the internal LV diameter and the peak velocity of circumferential fiber shortening were reduced in CHF patients (p less than 0.01 and 0.0001), while the percentage thickening of the LV posterior wall (PW) and interventricular septum (IVS), were independent of CHF presence. LVPW relaxation and indices of the overall diastolic LV function had similar values in all groups. The relation of all systolic and diastolic indices to BU was low (r less than 0,6) and in most cases indifferent (p:NS). A special finding was observed in 4 CHF patients, where segmental IVS dyskinesia contrasted with a satisfactory LVPW motion. The above results indicate that CHF in beta-thalassemia is not the consequence of volume and iron overload, but that these factors are predisposing towards the development of a specific type of cardiomyopathy.