Background: Heart failure is a significant problem causing morbidity and mortality in children with acyanotic CHD left-to-right shunt. Congenital heart disease is often associated with ventricular dysfunction, volume or pressure overload, resulting in a high risk of heart failure. N-Terminal-pro-Brain Natriuretic Peptide (NT- pro-BNP) is a biochemical marker in the left ventricle, which is used as a diagnostic marker for adult heart failure since it has depicted a significant correlation between heart failure and elevated levels of NT-pro-BNP. This study aimed to analyze the relationship between NT-pro-BNP levels and heart failure in children with acyanotic CHD left-to-right shunt. Methods: An observational analytic examination with a cross-sectional study design was conducted on children aged 1 month to 18 years with acyanotic CHD left-to-right shunt with suspected heart failure at the Pediatric Cardiology Outpatient Clinic, Emergency Department, and Pediatric Ward of Dr. Soetomo General Hospital Surabaya from September 2020 to March 2021. Statistical analysis was carried out using Mann-Whitney test and contingency correlation test of Chi-Square with a significance value of p < 0.05. Results: There were 43 subjects fulfilling the inclusion criteria in which 53.5% of them were female with a mean age of 48 months. Furthermore, the most common type of acyanotic CHD left-to-right shunt with heart failure was VSD, followed by ASD and PDA. There was a significant relationship between increasing NT-pro-BNP levels with heart failure with p < 0.001 based on chi-square test with moderate correlation strength (r = 0.57) based on the contingency correlation test. Conclusion: There is a significant positive correlation between NT-pro-BNP and heart failure in children with acyanotic CHD left-to-right shunt.