Abstract The purpose of this study is to study the role of vitamins and trace elements in the prevention of cardiovascular diseases (arrhythmias) in children. In 2015-2019, 300 children of the experimental group, 141 girls and 159 boys with diseases associated with heart dysfunctions were examined. The average age of children is 11.2±1.2 years, the interval is from 6 to 16 years. The second, control group included 150 healthy children, 81 boys and 69 girls, the average age of the child in this group was 11.6±1.2 years. Children from the control and experimental groups lived in the same city (Orenburg, Russia; Grozny, Russia), in identical climatic (environmental) conditions. The concentration of trace elements in the hair and the level of vitamin D, B9 and B12 in the blood was determined using the method of atomic emission spectrometry and the immunochemical method, respectively. A 1.4-fold higher frequency of occurrence of vitamin D deficiency or deficiency was found in the experimental group (p≤0.001). As for the deficiency of vitamins from group B, it was detected exclusively in patients with impaired heart function. Calcium deficiency was found in 267 children from the experimental group (89%) with cardiac abnormalities compared with 60 children from the control group (40%, at p≤0.001). A similar trend was recorded for magnesium: deficiency was found in 270 children (90%) from the experimental group with a deficiency of vitamin D compared with 51 (34%) children from the control. (p≤0.001). The values of Pearson correlations (at p≤0.05) between the deficiency of vitamin D and the low concentration of the chemical elements, in particular, calcium (0.95), magnesium (0.92), manganese (0.89), phosphorus (0.87), zinc (0.84), were obtained. For four elements, the dependences were obtained between a low concentration of vitamin D and an increased concentration of these elements: lead (0.89), strontium (0.83), nickel (0.84), and aluminum (0.79). In children with cardiac abnormalities, the concentration of vitamins is 1.5–2 times or more significantly lower compared to the control group. For the risk of disturbances in the heart, a concentration of vitamin D at a level of 21.8 ng/ml is sufficient, which slightly exceeds the minimum permissible concentration of this vitamin. Since most of the chemical elements we studied are somehow related to the concentration of vitamin D, the determination of the critical concentration of this vitamin seemed extremely important. Children with vitamins D, B9 and B12 deficiency, have heart problems more often than the healthy children of the same age and living in similar conditions. For a third (5 out of 18) of the studied chemical elements there is a direct correlation between their low concentration and low concentration of vitamin D in the blood plasma. For 4 elements, a high concentration was established in conditions of a lack of vitamin D (lead, nickel, strontium, aluminum). A high risk of arrhythmia may be associated with a concentration of vitamin D not exceeding 21.8 ng/ml.