Heart disease is the primary cause of death in patients with beta-thalassemia major. The study aimed to determine the association between vitamin D and left ventricular function in patients with beta-thalassemia major with iron overload. A cross-sectional hospital-based study was conducted, where the vitamin D and ferritin levels of children living with beta-thalassemia major were measured, and left ventricular function was assessed utilizing ejection fraction (EF) and fractional shortening (FS) using 2D echocardiography. The mean serum ferritin was 4622 ± 2289 ng/ml, and the mean serum vitamin D levels were 22 ± 7.7 ng/ml. The mean values of EF were 62.30 ± 6.9%, and FS was 31.21 ± 4.8%. Statistically significant negative correlation (r= −0.447,p< 0.001) was found between vitamin D and serum ferritin values, and a significant positive association was found between vitamin D levels concerning EF and FS with a p-value of 0.034 and 0.014, respectively.Conclusion: It was observed  that increasing ferritin was associated with lower vitamin D levels which in turn influenced fractional shortening /cardiac function in these patients.What is Known:• Patients with Beta Thalassemia major on long term transfusion are prone to develop heart disease / cardiac failure due to chronic iron overload.What is New:• Patients with beta thalassemia major on long term term transfusions with iron overload who are vitamin D deficient are more prone to the cardiac complications which inturn can be prevented by vitamin D supplementation.