Introduction to ECG: The beating of the heart is mainly controlled by the sinus node located above the right atrium which is the direct command of the heart. The sinus node automatically generates excitation, which is rapidly transmitted to all parts of the heart in the form of bioelectricity along a special conduction system. The heart muscle receives the excitation signal and produces a corresponding series of electrical activities that cause it to contract. Although this series of electrical activity is very weak, it still travels to the surface of the body. If we place electrodes on different parts of the body surface to amplify these weak electrical activities and then record them, a graph reflecting the heart’s activities can be shown, which is called ECG. The clinical significance of electrocardiography: 1, to identify the nature of the arrhythmia The doctor with a stethoscope to listen to the heart or feel the pulse, can only be found irregular heart rhythms, but what kind of nature of the disease? Is the “command” sinus node failure? Or is it a lesion in one of the conduction systems? Only rely on the electrocardiogram to help make a clear judgment. 2.Diagnose atrial and ventricular hypertrophy The heart is divided into four parts, the upper part is the right and left atria, the lower part is the right and left ventricles, the electrocardiogram can help to diagnose which one (or two) atria or ventricles are hypertrophied. 3, can quickly reflect the site of myocardial infarction and myocardial ischemia, the degree of strain can also help diagnose myocarditis, cardiomyopathy, pericarditis. The diagnosis of congenital heart disease has very important value. 4, cardiac monitoring monitoring of critically ill patients (including cardiac surgery), can be found at any time whether the heart is abnormal. 5, to understand the efficacy of drugs and their effects on the heart muscle For example, the use of digitalis in the treatment of heart failure, the use of a variety of drugs to treat arrhythmia, etc., are required to carry out regular electrocardiogram dynamic observation. 6.Diagnose electrolyte metabolism disorders In the absence of conditions for biochemical determination, hypokalemia, hyperkalemia and hypocalcemia have specific changes on ECG.