A “residual shunt” is a “small hole” that remains after surgery. “, “after arterial catheterization” or “after repair of other complex precordial disease with septal defect”. According to the literature, the incidence of “residual shunt after defect repair” is about 5%. The main reasons for this are as follows. (1) The septal defect is often a combination of several defects, and the longitudinal and transversal intersection of the muscle bundles makes it impossible to expose clearly during surgery, and only part of the defect may be sutured during surgery, leaving some residual. (2) Suture avulsion. The incidence is higher in the repair of large or high septal defects. To prevent damage to the surrounding normal tissues (conduction, valves, and tendons of the heart) during repair, sutures are placed only in the superficial layers of the defect, and as the heart resumes beating, some of the sutures are torn out as the pressure in the heart chambers increases, resulting in residual shunts. (3) In patients with pseudoventricular wall tumor formation, the opening appears to be small but the base is large, and residual shunts often occur after surgery when only the opening is sutured closed. (Pseudoventricular wall tumor means that the opening of the ventricular septal defect is larger, and with the continuous impact of blood flow, the fibrous tissue at the edge of the defect proliferates and forms a tumor-like protrusion, and the opening looks smaller but actually has a larger base.) (4) Infection occurs after surgery, such as bacterial endocarditis, and once infection occurs around the patch after surgery, the suture often tears off at the suture, causing a partial residual shunt. (5) The residual shunt after arterial catheterization is due to the fragility of the catheter tissue, which may cause a small amount of residual in the center of the lumen due to excessive force during the ligation. Or the lumen may reopen after ligation. A good tip: The presence of residual shunts is diagnosed by cardiac ultrasound or cardiac catheterization. Small residual shunts (<3mm) generally do not require surgical management and will close spontaneously in more than 50% of patients after six months. A small percentage of patients fail to close on their own and are generally left untreated if they do not enlarge. Residual defects with larger shunt volumes or increasing residual shunts often require reoperative treatment.