Background: Beta-thalassemia major is a severe and lethal hemolytic anemia. Regular transfusion is necessary for avoidance of its complications but it may end to cardiac involvement secondary to iron overload. Angiotensin converting enzyme inhibitors (ACEIs) are useful medications even in early stages of heart failure. We studied the effects of two common ACEIs on improvement of heart function in asymptomatic patients with beta thalassemia. Methods: Of 300 patients over 10 years old with beta-thalassemia, 62 asymptomatic patients were divided into two groups. Captopril (1mg/kg/d in 2-3 divided doses) was started for patients in group one and enalapril (0.1 mg/kg once daily) was started for patients in group two. Six months later, systolic and diastolic parameters were assessed and compared with those before treatment with ACEIs in each group and after treatment between the two groups. Results: In group one, left myocardial performance index, ejection fraction and fractional shortening were improved significantly (P<0.001). Decrease in peak atrial velocity and increase in early maximum filling velocity/atrial velocity (E/A) ratio of mitral valve were also significant (P=0.04 and P=0.01 respectively). In group two, a significant improvement in myocardial performance index, ejection fraction, and fractional shortening was seen compared with before treatment (P<0.001). Also peak early maximum filling velocity of mitral valve and peak atrial velocity of tricuspid valve were improved. Comparison of the two groups after treatment with ACEIs did not show any difference, although both of them showed significant improvement. Conclusion: In patient with beta-thalassemia major early administration of ACEIs is recommended. Since the difference between the efficacy of captopril and enalapril was not significant, both drugs seem to be suitable in these patients.