Abstract : Hemolysis and regular blood transfusions as the long-term beta thalassemia major treatment can cause iron accumulation and damages these organs, potentially causing death. Iron accumulation in the heart muscle decreases ventricular function and may progress to cardiomyopathy and heart failure. Serum ferritin concentration can determines iron stores in the body. Heart failure can be indicated by cardiac markers, such as troponin. This research was an analytical cross-sectional study conducted to observe the relationship between serum ferritin and troponin I levels in children with beta thalassemia major receiving blood transfusion, particularly at Haji Adam Malik hospital, Medan, Indonesia. Univariate analysis was used to asess the mean levels of serum ferritin and troponin I. Bivartiate analysis was used to assess the relationship between serum ferritin level and troponin I level, where Pearson correlation test for normal distribution data or Spearman correlation test for abnormal data distribution. The mean serum ferritin level was 7233.26 ng/mL. The majority of the research subjects had serum ferritin level above 1000 ng/ml. There was only 1 child (1.5%) with serum ferritin level below 1000 ng/mL. The mean troponin I level was 5.97 ng/mL. Almost two third (41 / 62.1%) of the research subjects had troponin I level above 0.8 ng/mL, while the remaining research subjects (25 / 37.9%) had troponin I level below 0.8 ng/mL. There was a significant relationship between serum ferritin level and troponin I level in children with beta thalassemia major at Haji Adam Malik hospital, Medan, Indonesia (p <0.001).