Objective: Children with congenital heart disease are at risk of malnutrition due to inadequate calorie intake, increased energy expenditure, pulmonary infections, and malabsorption. The aim of this study was to investigate the changes in appetite, nutritional hormones, and anthropometric measurements before and after the transcatheter closure of the atrial septal defect. Method: The study included 27 patients whose atrial septal defect closed percutaneously and 25 children as a healthy control group. The initial symptoms, anthropometric measurements, and laboratory tests were recorded initially, and 1 month and 6 months after the closure. Results: The mean age of patients and control group were 88.29 ± 58.25 months, 86.52 ± 55.81 months respectively. At the 1st month after the closure, all the symptoms in the patient group decreased compared to the initial visit except rapid breathing (p <0.05). The percentage of patients who had a lack of appetite decreased from 45% to 5% at the 1st month visit. After the closure, the increase in weight for age, body mass index, and z-score were statistically significant at the 1st and 6th months (p <0.05). Insulin-like growth factor-1 levels increased compared to the initial values at the 1st month (p =0.016). A linear decrease in ghrelin levels and a linear increase in leptin levels were observed in the atrial septal defect group during the 6-month follow-up after the closure. Conclusion: Children with atrial septal defect are at the risk of malnutrition. The primary prevention of malnutrition should be the goal of our treatment plan for these children; the timing of the interventional treatment is critical and has to be before the development of malnutrition.