The objective of this research was to assess the correlation between vitamin D levels and heart failure in children. Vitamin D is a micronutrient affecting the prognosis for heart failure in children. Vitamin D deficiency exacerbate heart failure condition. Moreover, in severe heart failure functional class, vitamin D deficiency is commonly reported. This research was an analytical cross-sectional research carried out in pediatric cardiology polyclinic and inpatient clinic Haji Adam Malik Hospital Medan from September 2020 ? January 2021 to assess the correlation between vitamin D levels and heart failure. Vitamin D level assessment was done to 50 pediatric patients with heart failure. Correlation test was done by using Somers? D correlation tests by SPSS 17.0 software. Among 50 research subjects, 40 subjects (80%) suffered from vitamin D deficiency and 14 of them (35%) were classified in class III heart failure. By using Somers? D correlation test, non-significant relationship was observed between vitamin D levels and heart failure conditions (p=0.337; r = -0.079).