The biventricular systolic function was evaluated by M mode and Doppler echocardiography in 16 patients with homozygous beta-thalassemia and beta-thalassemia Hb E disease, aged 5-14 yrs (9.9 +/- 2.4 yr). The left ventricular end-diastolic dimension and left ventricular mass were increased in 88 per cent of the patients. Left ventricular fractional shortening and cardiac index were normal in all but one patient. Fifteen patients had evidence of pulmonary artery hypertension manifested by abnormality in the ratio of right ventricular acceleration time to ejection time (AT/ET). There was good correlation between platelets count and AT/ET (r = -0.70, P = 0.002). Thrombocytosis was noted in 4 patients. Our findings indicated that in beta-thalassemic children, right ventricular dysfunction was detected earlier than left ventricular dysfunction and platelets may play a role in the pathogenesis of pulmonary artery hypertension.