I often encounter patients who come to the clinic with a physical ECG and ask, “Doctor, I have an abnormal ECG on my physical exam, and it says it’s pre-excitation, but I don’t have any special discomfort, do you think I need treatment?” In the emergency room, we also encounter patients with tachyarrhythmias who have recovered their sinus rhythm with medication or electrical resuscitation, and then the ECG indicates a pre-excitation syndrome. So what exactly is preexcitation and preexcitation syndrome? Do they require treatment? The conduction system of the heart is composed of special myocardium responsible for the formation and conduction of normal cardiac impulses, including the sinus node, inter-nodal bundle, atrioventricular node, Hitchcock’s bundle, right and left bundle branches, and Purkinje fibers. The cardiac conduction system is like a conduction pathway that transmits electrical impulses from the sinoatrial node from the atria to the ventricles, thus completing a cardiac cycle. The atrioventricular node is like a roadblock in this pathway, limiting the speed of conduction of the electrical impulses. However, in some people, there are “abnormal additional shortcuts” in the cardiac conduction pathway, which can also conduct the impulse signal faster than the normal atrioventricular conduction system, and often the ventricular excitation is transmitted from the atrioventricular node and Often, the ventricular excitation is caused by two parts of the impulse from the atrioventricular node and the “shortcut”, i.e., the QRS wave is a fusion wave. Therefore, the so-called “preexcitation” is the premature excitation of part or all of the ventricle by electrical impulses, and these “shortcuts” are the anatomical basis for the occurrence of preexcitation. According to large-scale population statistics, the average incidence of preexcitation syndrome is 1.5 per 1,000, and most patients with preexcitation syndrome do not have organic heart disease, and some have a familial tendency. It can be detected at any age by physical examination of the ECG or by episodes of tachyarrhythmia, mostly in men. Preexcitation syndrome can be complicated by congenital cardiovascular diseases such as tricuspid valve subluxation, mitral valve prolapse, and cardiomyopathy. Preexcitation itself does not cause symptoms, and those with preexcited ECG manifestations and increases with age. Tachycardia develops as atrial fold tachycardia, as atrial fibrillation, as atrial flutter. We should be alert to tachycardia with excessive frequency, especially persistent episodes of atrial fibrillation, which can deteriorate into ventricular fibrillation or lead to congestive heart failure and hypotension. Due to the different “shortcuts”, the performance characteristics of preexcitation ECG vary, but the most common manifestations are: 1. P-R interval less than 0.12 seconds. 2. 2. QRS time limit is greater than 0.11 seconds. 3, QRS wave group start stuttering, called delta wave. 4, P-J interval is normal. 5.Secondary ST-T changes. Some patients have normal ECG. If there is no tachycardia episode, it is difficult to confirm the diagnosis based on the body ECG, which we call invisible pre-excitation, and often need to confirm the diagnosis by intracardiac electrophysiological examination. In terms of treatment, if the patient has never had an episode of tachycardia, or has occasional episodes with mild symptoms, no treatment is needed for the time being and observation can be continued. If tachycardia is frequent with significant symptoms, treatment should be given promptly, including drugs and radiofrequency ablation. In patients with pre-excitation syndrome with episodes of atrial flutter or atrial fibrillation, immediate electrical cardioversion should be given if dizziness or hypotension occurs. In conclusion, when a patient is diagnosed with preexcitation syndrome due to a physical examination or the occurrence of tachycardia, he or she should promptly go to the cardiology department for further consultation and treatment to clarify the type of preexcitation syndrome and the location of the “shortcut”. At present, with the rapid development of medical technology, radiofrequency ablation has long been the treatment of choice for preexcitation syndrome with tachycardia, and it is safe and eliminates the need for oral antiarrhythmic drugs to prevent attacks.