Preexcitation syndrome includes type A preexcitation syndrome and type B preexcitation syndrome. Compared with type A preexcitation syndrome, type B preexcitation is not more severe. The main danger of both syndromes is that they can cause supraventricular tachycardia, such as sudden onset of severe arrhythmias, and the heart rate can reach 250-350 beats per minute after jumping. This kind of patients may be more difficult to treat than type A pre-excitation, but compared with type A pre-excitation, they are treated in a similar way and can be cured by radiofrequency ablation. However, the recurrence rate of type B pre-excitation is higher, and it is not easy to succeed. The possibility of multiple bypasses is greater in this group of patients, which means that they often have many combined bypasses, often three or four type B pre-excitations exist at the same time, and the success rate is relatively lower. It is not more severe than type A.