24 patients with aneurysm of the membranous ventricular septum were confirmed by operatively in our hospital. Four patients had true aneurysm of the membranous ventricular septum, and 20 false. According to the difference of membranous aneurysm (true or false) and the size of the defect, different methods of the operation were adopted. Postoperation intracardiac residual shunt was avoided. There was no death in the group. Follow-up for 9 years to 6 months showed excellent long-term results. The authors consider that the diagnosis of this disease before operation is difficult.