Cardiac complications are the leading cause of death in β-thalassemia major (TM) patients. The aim of this study was to investigate the impact of iron overload on ventricular functions using conventional and tissue Doppler imaging (TDI) in patients with TM and compare them with children with thalassemia trait (TT) and healthy controls. This prospective study includes 3 groups: group 1: 29 patients with β-TM; group 2: 28 patients with TT; group 3: 29 healthy controls. Peak late relaxation velocity determined by conventional echocardiography for the right ventricle was significantly higher and the E/A ratio for the right ventricle and left ventricle were significantly lower in TM patients than the other groups (P < .05). Peak late relaxation velocity determined by TDI for the left ventricle, interventricular septum, and right ventricle were significantly higher in TM patients than the TT subjects and controls (P < .001). The E/A ratio determined by TDI for the left ventricle, interventricular septum, and right ventricle were significantly lower in group 1 than the other 2 groups (P < .001). There was a negative correlation between the ferritin level and E/A ratio for the left ventricle, interventricular septum, and right ventricle using TDI (P < .05). Conventional echocardiographic techniques have failed to distinguish ventricular functions of asymptomatic patients with TM from the subjects with TT and from normal controls when global functions were examined. The present study indicates that TDI should be used for screening of TM and TT subjects' cardiac functions.