The following principles should be followed in the diagnosis of electrocardiogram: First, the source of the heartbeat should be clearly identified, whether the pacing point of the heart originates from the sinus node, atrium, ventricle or other parts of the heart; at the same time, the rhythm of the heartbeat should be paid attention to whether it is neat or not. Secondly, the presence of bradycardia or tachycardia should be determined by the distance between RRs: if it is less than 3 frames, it means tachycardia, if it is more than 5 frames, it means bradycardia. Third, pay attention to the analysis of P waves, especially to clarify the width, amplitude and direction of P waves; in addition, pay attention to check whether the PR interval is neat to clarify the presence of atrioventricular block and other conditions. Fourth, pay attention to the analysis of ST segment and T wave to clarify the presence of myocardial ischemia and myocardial infarction and other related conditions. In addition, the electrical axis, QRS wave time frame, amplitude, etc. should be analyzed.