Before the heart produces a contraction, its cardiomyocytes, a “little power plant”, can autonomously emit a regular bioelectric current, which then initiates myocardial contraction and diastole. These weak bioelectrical currents can be conducted in all directions along the tissues of the organs surrounding the heart to the skin. Doctors using ECG machine’s can press and place electrodes through the prescribed positions and record a special graph called ECG. If the process of power generation and conduction in the heart muscle cells is not normal, it will show abnormal ECG changes. Whether there is a disease or not, the doctor can make the appropriate diagnosis based on a full range of judgment. Electrocardiograms are very important in guiding the diagnosis and treatment of disease. Patients with heart disease and certain people who do not have heart disease but who require ECG testing often need to have their ECGs reviewed on a regular basis. Electrocardiogram is mainly used to confirm the diagnosis of myocardial infarction and arrhythmia, for which the diagnosis can be made almost 100%; it can also be used to assist in the diagnosis of coronary artery disease, cardiomyopathy, myocarditis, heart valve disease, congenital heart disease, hypertension, pulmonary heart disease, as well as monitoring the process of medication and surgical procedures, and so on.