Electrocardiogram (ECG) is one of the most common tests prescribed by cardiologists. As soon as a patient develops symptoms such as chest tightness, chest pain, palpitations, etc., the doctor will give him/her a copy of the ECG immediately. Through ECG examination can quickly diagnose a considerable part of the heart disease, such as: 1, arrhythmia; 2, myocardial ischemia, myocardial infarction, to determine the location of myocardial infarction. 3, diagnosis of cardiac enlargement, hypertrophy. 4, to determine the effect of medication or electrolyte condition on the heart. 5, to determine the status of the artificial cardiac pacing, and so on, so the clinical application of a wide range. Recently, a friend asked me if repeated ECGs would cause damage to the body, and whether there is any harm for pregnant women and children to have ECGs. Our answer is: ECG examination does not cause harm to the human body. By definition: An electrocardiogram (ECG or EKG) is a technique that utilizes an electrocardiogram machine to record from the body’s surface a graphic representation of the changes in electrical activity produced by the heart with each cardiac cycle. Why can ECG machines diagnose diseases? The electrical activity necessary for the existence of the heart, in humans and in any other living creature, is primarily the depolarization and repolarization of the cardiomyocytes. And an ECG machine is actually a recording instrument, connected to the body by electrode pads, that records this weak electrical activity produced by the heart. Because the signal generated by this electrical activity is so small, it needs to be amplified by the ECG machine, and through the function of “filtering noise”, a clear ECG is finally presented to the doctor. So the ECG machine is actually an instrument that records the electrical activity of the human heart without interfering with the human body in any way. Therefore, ECG is a “non-invasive” test. Any electrical appliance that is connected to electricity may leak current through the body and into the ground. If the leakage current is too large, it may lead to electric shock to the examinee. Therefore, in order to further ensure patient safety, the application of medical electrical equipment often has isolation measures, photoelectric coupling, electromagnetic wave coupling. The current leakage current of the chassis power supply of the ECG machine should be less than 100uA. as long as it is from a regular hospital and undergoes regular maintenance, the ECG machine must be very safe. For pregnant women, children and other special groups of people, ECG examination is also very safe, there is no ECG “radiation” or “damage” occurs. Today’s knowledge point: ECG will not cause damage to the human body, if you have symptoms of discomfort, you need to cooperate with the doctor as soon as possible to carry out ECG examination, early detection of disease, early treatment.