The possible risks of mitral valve balloon dilatation arise from three sources: (1) those directly related to balloon valve expansion. These include: (1) Severe mitral valve insufficiency, which can lead to acute left heart failure and necessitate emergency surgical valve replacement if necessary. Mild to moderate mitral valve insufficiency is common in mitral balloon dilatation, is not a complication, and usually poses no risk to the patient. (ii) Cerebral embolism or transient syncope. (iii) Severe arrhythmias. (iv) Balloon rupture. ⑤ Acute left heart failure. Among the above risks, mitral valve insufficiency is relatively common. (2) Risks associated with atrial septal perforation. These include: ① Cardiac perforation, which can lead to pericardial tamponade and require urgent surgical repair in severe cases. ② atrial septal defect, the use of polyethylene balloons (much used in Europe and the United States and other countries, now tends to be eliminated) is more obvious; but the use of the currently commonly used Japanese imports called Inoue balloons is rare, and even if there is, the degree is very mild and does not bring harm to the patient. (3) Risks associated with routine catheterization. There can be: ① bleeding at the puncture site, including subcutaneous ecchymosis and hematoma. (2) Puncture site pseudoaneurysm, arterial entrapment, etc. (iii) Arteriovenous fistula at the puncture site. (iv) Thrombosis and embolism, etc. Although we list many of these risks, mitral balloon dilatation is actually a very safe procedure with a less than 1% incidence of serious complications.