Sinus rhythm normal ECG to identify heart rate, rhythm, p-wave, PR interval, QRS wave, ST segment, T wave, U wave, etc.. 1. Heart rate: Quiet heart rate <60 beats per minute is bradycardia, >100 beats per minute is tachycardia. 2. Rhythm: whether RR or PP intervals are equal. 3. p-wave: obtuse round, upright in leads I, II, aVF, V4~V6, inverted in lead aVR. Duration <0.12 s, amplitude <0.25 mv in limb leads, <0.2 mv in thoracic leads. p-wave amplitude is increased in right atrial hypertrophy, and p-wave duration is prolonged in left atrial hypertrophy. 4. PR interval: lasts 0.12-0.20 seconds. Prolongation can be seen in atrioventricular block and shortening can be seen in preexcitation syndrome. 5.QRS wave: ≤0.12 seconds, amplitude V1 lead ≤1mv, V5, V6 lead ≤2.5mv. Wide aberration is seen in intraventricular differential conduction, premature ventricular contraction, ventricular tachycardia, etc.; V1 lead＞1mv is seen in right ventricular hypertrophy, V5, V6 lead＞2.5mv is seen in left ventricular hypertrophy. 6.ST segment: except for V2 and V3 leads, which can be elevated significantly, up to 0.2mv or even higher, the ST segment of the remaining leads is basically the same as the baseline level, and the depression of any lead is ≤0.05mv. Exceeding this range of elevation or depression is seen in myocardial ischemia. 7.T wave: amplitude ≥1/10 of R wave in the same lead, too low is seen in myocardial ischemia. 8. U-wave: generally not more than 1/2 of the T-wave in the same lead, increased U-wave can be seen in hyperkalemia. ECG needs to be recognized and diagnosed by a doctor and self-diagnosis is not recommended.