Whether or not lactate dehydrogenase above 400 U/L is serious is related to the cause of the elevated lactate dehydrogenase. If it is caused by colds, strenuous exercise, etc., it is usually not serious; if it is caused by liver disease, heart disease, etc., it is more serious. 1. Colds: Lactate dehydrogenase 400 U/L is usually mildly high. If a cold occurs, some cold viruses will directly invade the heart muscle and cause myocardial damage, which can be accompanied by elevated lactate dehydrogenase. Symptoms will resolve with active treatment of the cold. 2. Strenuous exercise: Lactate dehydrogenase exists in the cytoplasm of all tissue cells in the human body, the highest content of which is skeletal muscle, if it is after strenuous exercise, lactate dehydrogenase will be mildly high, which is a normal physiological phenomenon, and it will drop to the normal level after appropriate rest. 3. Liver disease: Lactate dehydrogenase up to 400U/L may be related to liver disease, such as chronic hepatitis, liver cancer. Liver disease can easily lead to liver cell damage, and the lactate dehydrogenase in the liver cells will be released into the blood, thus causing the lactate dehydrogenase value to rise. 4. Heart disease: Acute myocardial infarction, rheumatic myocarditis, viral myocarditis and other heart diseases may also lead to lactate dehydrogenase value of more than 400 U/L. In short, lactate dehydrogenase 400 more if liver disease, heart disease caused by more serious, should promptly consult a doctor, do further examination, identify the causes, and active treatment.