Since its invention at the beginning of this century, ECG has become an indispensable auxiliary test for the diagnosis of cardiovascular diseases and monitoring of critically ill patients. The specific clinical applications include: 1. The diagnosis of cardiac arrhythmia has a definite value. The electrical excitation of the heart is sent out from the sinus node and is conducted to all parts of the heart through the conduction system according to a certain frequency, sequence and speed. If there is an abnormality when the electrical excitation is issued or during conduction, it will cause arrhythmia, and also further to other classes, which is important for clinical diagnosis and treatment. 2.The diagnosis of coronary heart disease myocardial infarction has high accuracy, it can not only determine the presence or absence of myocardial infarction, but also determine the stage, location, scope and evolution of the infarction. 3.It is more helpful for the diagnosis of atrial hypertrophy, myocarditis, cardiomyopathy, coronary artery supply deficiency, pericarditis and pericardial effusion. 4.It helps to understand the effect of certain drugs, such as digitalis, quinidine, insulin, antimony, etc. on the heart, helps to diagnose and adjust the treatment plan of certain drugs, and is meaningful for the selection of dosage and usage of certain drugs and the judgment of their efficacy. 5, to help diagnose human blood electrolyte disorders, such as high and low potassium and high and low calcium disorders. 6.Electrocardiogram has absolute diagnostic value for abnormal heart position, such as right-sided heart. 7.To determine the effect of certain diseases on the heart, such as rheumatic fever, connective tissue disease, viral and mycoplasma infections, acute infectious diseases, malnutrition, etc. 8.Electrocardiogram can be used as a kind of temporal marker of cardiac telecommunication information, often traced simultaneously with cardiac function measurements such as phonocardiogram, echocardiogram, impedance hemogram and other cardiac electrophysiological studies to facilitate the determination of the temporal phase of the cardiac activity cycle. 9.Electrocardiogram monitoring has been widely used in surgical anesthesia, medication observation, aerospace and sports, and other cardiac monitoring and rescue of critically ill patients. 10.To assist in the etiological diagnosis of syncope of unknown cause.