To determine whether the ECG is normal, it is necessary to recognize whether the frequency, rhythm, and P wave, PR interval, QRS wave, ST segment, T wave are normal. 1. Normal adult heart rate is 60~100 beats/minute in quiet state. <60 beats/min is bradycardia, >100 beats/min is tachycardia. 2. Whether the heart rhythm is regular, i.e., whether the RR interval is consistent. 3. Normal P wave: bluntly rounded, duration generally <0.12 seconds, <0.25mv in limb leads, <0.2mv in chest leads, upright in I, II, aVF, V4~V6 leads, inverted in aVR leads. 4. Normal PR interval: time between 0.12 and 0.20 seconds. 5. Normal QRS wave: generally not more than 0.11 seconds, amplitude V1 lead ≤ 1mv, V5, V6 lead ≤ 2.5mv. 6. Normal ST segment: V1~V3 leads can be elevated by 0.1~0.3mv, and ST segment of the remaining leads is basically consistent with the baseline. 7. Normal T wave: the direction of the main wave is the same as the QRS wave, and the amplitude is not less than 1/10 of the R wave in the same lead. The normal or not of ECG needs to be recognized and diagnosed by professional doctors.