Electrocardiogram is a clinical examination that records the physiological electrical activity of the heart by means of an electrocardiogram machine. The most common type of electrocardiogram in the ward is the single-lead monitor electrocardiogram, and the most common type in the outpatient clinic is the 12-channel electrocardiogram. There are various types of examination, such as load ECG, including exercise load ECG and drug load ECG; and ambulatory ECG, with 24-hour, 48-hour, and 72-hour. In addition, there are intraesophageal ECG, intracardiac chamber ECG examination and so on. The basis of diagnosis is mainly through the 14 data generated during ECG acquisition. These 14 data are the time of the waveforms, the voltage amplitude and the direction of the waveforms. The most accurate diagnostic disease is arrhythmia, but it can also provide diagnostic clues for many diseases, such as myocarditis in children, congenital heart disease, and the physiological changes in function caused by vegetative nerve dysfunction in adolescence. There are also hyperthyroid heart diseases caused by hyperthyroidism, such as atrial fibrillation. Myocardial ischemia, hypoxia, caused by a variety of coronary heart disease, acute infarction, persistent chronic myocardial ischemia and so on. Hypertensive heart disease caused by high blood pressure can provide certain clues; ionic changes in renal disease, such as hyperkalemia, hypokalemia, are reflected on the electrocardiogram. Pulmonary heart disease, such as heart disease caused by chronic bronchitis in the later stages, can provide some clues. Particular attention should be paid to the fact that in the course of advancing years, as one gets older, the conduction bundles are gradually aging and the chances of arrhythmias increase. For example, the most common arrhythmia is ventricular pre-systole, also known as premature ventricular contractions. There is also atrial fibrillation, which we must be concerned about. Atrial fibrillation peaks at the age of 75, and the consequences of atrial fibrillation are very scary, such as the ability to form blood clots. If it embolizes in the brain, it’s a cerebral thrombosis; if it embolizes in the heart, it’s a heart stroke. There are also congenital disorders, such as Brugarda’s sign or congenital hypoplasia of the right ventricular muscle.