LDH, or lactate dehydrogenase, is widely found in various tissues of the human body, in fact, it is most evident in cardiac and skeletal muscle cells as well as blood and liver. High LDH in children may be a physiological phenomenon, or it may be caused by damage to the heart muscle and liver cells. 1. Physiological factors: slight elevation may be caused by machine detection error or individual differences, if there is no other discomfort, this situation only needs to be observed and followed up. 2. Myocardial damage: When children are infected by viruses, it is easy to cause myocarditis or myocardial cell damage, and LDH will be elevated accordingly, which can be diagnosed together with other cardiac enzymes, i.e. ECG. 3. Hepatocyte damage: When children are infected by EBV and suffer from infectious mononucleosis, the hepatocytes are damaged and the LDH inside is easily released. There are other causes of high LDH in children, such as pulmonary infarction and hypothyroidism. It is recommended that if there are any other symptoms or if the LDH is significantly elevated, it is important to seek medical attention to find the cause and treat it accordingly.