Preexcitation syndrome refers to the presence of another channel between the atria and the ventricles that causes the atrial excitation to travel down through this abnormal channel before it can travel down through the atrioventricular node to the ventricles, causing premature excitation of the ventricular muscle. Intermittent preexcitation syndrome is an intermittent preexcitation wave-like electrocardiogram change. The basis of preexcitation is the premature excitation of part or all of the ventricle by atrial impulses. The anatomical basis for the occurrence of preexcitation is the presence of special conduction tissues of the atria, in addition to some general working cells and myocardial bundles that connect the atria to the ventricles, mostly the kent bundles, in addition to the atrial Schiff’s bundle junctional ventricles and fibrous branching ventricular fibers. In addition to the normal pathway, there is an abnormal bypass, and the electrophysiological stimulus will be transmitted from the bypass to the ventricle in advance to contract the ventricular cells in advance, which is abnormal and may lead to tachycardia. Tachycardia can also occur in two ways: one is a retrograde tachycardia through the bypass antegrade or retrograde transmission; the other is a preexcitation combined with atrial fibrillation, where the electrical conduction of atrial fibrillation is competing from the bypass or from the normal atrioventricular node, resulting in a rapid ventricular rate and a wide QRS wave as a manifestation of preexcitation combined with atrial fibrillation arrhythmia.