The range of ECG critical values mainly includes the following aspects. 1. the manifestation of acute myocardial ischemia, especially the manifestation of suspected acute myocardial infarction after ECG, or the manifestation of suspected reoccurrence of myocardial infarction compared with previous ECG. 2. tachyarrhythmias, mainly including ventricular flutter and ventricular fibrillation. 3. Ventricular tachycardia of more than 150 beats per minute, supraventricular tachycardia of more than 200 beats per minute, tip-twisting ventricular tachycardia and pre-excitation with atrial fibrillation, etc. 3. Slow arrhythmias, such as heart rate less than 35 beats per minute. Accompanied by dizziness, chest tightness, blackness in front of the eyes and other symptoms, heart stopping for more than 3 seconds without any discomfort, heart stopping for more than 5 seconds is a serious slow heartbeat. 4, other conditions, such as severe hyperkalemia, severe hypokalemia, ECG manifestations of pulmonary embolism, T-wave electrical alternation found from ECG, special types of premature ventricular beats R-ON-T, etc. should be treated as ECG critical values.