The purpose of this study was to evaluate young asymptomatic patients with thalassemia major by utilizing an echocardiographic technique which traces an expanded image of the left ventricular posterior wall (LVPW). This technique separates global cardiac function from segmental changes in LV free wall thickness during systole and diastole. The study population consisted of 13 patients aged 2 to 15 years with classical homozygous beta-thalassemia. Thirty-one normal healthy individuals age 4 to 13 years served as controls. Echocardiograms, height, weight, and blood pressure were measured in all patients at their lowest hemoglobin level. Traces of the expanded LVPW were analyzed and measured; while total net thickening relative to baseline was similar in both groups at all times during systole and diastole, the LVPW in children with thalassemia was statistically thinner than in controls (p less than 0.001). Contraction was a nearly linear process in controls, but for patients with thalassemia, it was significantly faster at 50% and 75% of systolic time (p less than 0.05). Relaxation, on the other hand, was not linear for either controls or thalassemic patients. In both groups, diastolic thinning was biphasic; however, LV walls of thalassemic children thinned more slowly than normal for each time point in diastole (p less than 0.001). These results demonstrate that young children with thalassemia major, even if kept at strict transfusion and chelation regimens, have defects in LV segmental wall motion which antedate the appearance of clinical symptoms.