Abstract: Tetralogy of Fallot is a cardiac malformation with characteristic pulmonary artery stenosis and ventricular septal defect caused by right ventricular funicular or conus hypoplasia, including pulmonary artery stenosis, ventricular septal defect, aortic span and right ventricular hypertrophy. Dr. Xiao Yimin of Shanghai Yuanda Cardiothoracic Hospital introduced that infantile tetralogy of Fallot is a cardiac malformation with characteristic pulmonary artery stenosis and ventricular septal defect caused by right ventricular funicular or conus hypoplasia, including pulmonary artery stenosis, ventricular septal defect, aortic span and right ventricular hypertrophy. Infantile tetralogy of Fallot is composed of four cardiac malformations: 1. ventricular septal defect The defect is a perimembranous type defect and extends toward the outflow tract, mostly located under the aorta and sometimes below the pulmonary artery, called malalignment type ventricular septal defect. 2. Right ventricular hypertrophy is a secondary lesion. Among the above four malformations, only septal defect and right ventricular outflow tract stenosis are necessary. The septal defect must be sufficient to equalize the pressure between the right and left ventricles; right ventricular outflow tract stenosis is the main factor that determines the pathophysiology, severity and prognosis of the child. Furthermore, the stenosis may worsen over time. 3. Right ventricular outflow tract obstruction The stenosis may extend from the entrance of the right ventricular funnel to the left and right pulmonary artery branches. It can be funnel stenosis, arterial stenosis, or both. There is often dysplasia of the pulmonary valve annulus, common pulmonary artery trunk, and asymmetric stenosis of the pulmonary artery branches. The severity of the stenosis varies widely. In severe cases, pulmonary atresia may be accompanied by ductus arteriosus or collateral circulation vessels between the aorta and the pulmonary artery. The aortic root is thick and rotates rightward in a clockwise direction and rides over the ventricular septal defect, with a range of 15% to 95%.