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Background: Heart failure (HF) secondary to myocardial iron loading remains the leading cause of death in β-thalassemia major (β-TM) patients. The early diagnosis and treatment of HF in these patients is related to survival. We aimed to evaluate myocardial performance using conventional and tissue Doppler echocardiography and its relation to plasma NT-proBNP levels and iron overload indices in β-TM patients with preserved systolic function. Methods: The study population included 49 β-TM patients (24.0 ± 4.2 years) and 48 age-matched healthy controls. Doppler-echocardiographic study was performed and blood samples for NT-proBNP measurements were drawn on the third day following blood transfusion. Patients were divided as group-1, without diastolic dysfunction: E/E′ ratio < 9 and group-2, with suspected diastolic dysfunction: E/E′ ratio ≥ 9. Results: NT-proBNP levels and E/E′ ratio were increased in patients compared with controls (P < 0.001 and P < 0.001) but did not correlate with each other. A strong positive correlation was detected between NT-proBNP levels and mean ferritin levels in β-TM patients (rs= 0.939; P < 0.001). Median NT-proBNP levels were significantly higher in group-1 in comparison to controls [51.2 (41.51–113.5) vs 30.1 (17.97–68.16) ng/mL, P < 0.01]. NT-proBNP levels were also increased in group-2 in comparison to group-1 but this increase was not statistically significant. Conclusion: NT-proBNP secretion begins in the early phase of the disease before the increase in diastolic pressure becomes overt. While there was a strong correlation between the plasma NT-proBNP levels and iron overload, there was no correlation between NT-proBNP levels and diastolic dysfunction parameters in patients in the third decade of life. (Echocardiography 2012;29:318-325)