Atrioventricular Septal Defect (AVSD) is a not uncommon congenital heart disease, which refers to a septal defect between the mitral and tricuspid valves at the upper and lower differences in the location of the left and right attachments of the septum, including defects of the atrioventricular septum and malformations of the atrioventricular valve itself, which can manifest as two sets of atrioventricular valves retaining separate left and right atrioventricular orifices (primary orifice atrial defect) or a common atrioventricular orifice ( complete atrioventricular access). In this paper, we retrospectively summarized 21 cases of atrioventricular septal defect admitted to our hospital from 1980 to 2000, and summarized and analyzed their clinical data, so as to improve clinicians’ comprehensive understanding of this disease and achieve the purpose of early diagnosis and reasonable treatment. Data and methods 1. Subjects: The 21 cases of AVSD in this group came from more than 2600 children admitted to our hospital with congenital heart disease between 1980 and 2000 (0.81%), 12 males and 9 females, aged 2 hours to 11 years (average 40.66 months), of which 10 cases were partial AVSD, average age 6.1 years, and 11 cases were complete AVSD. The mean age was 4.37 months (among them, 10 cases had superior vena cava oxygen content of 1.4~3.3Vol%, except for 2 cases where the fractional flow could not be calculated because the oxygen content of each atrium was basically the same, but the remaining measured left-to-right fractional flow was 47~72.7% (mean 61.84%). Surgery: Five children with partial AVSD aged 5-11 years (mean 7.2 years) underwent radical surgery under hypothermic extracorporeal circulation, and autologous pericardial patches were given to close the atrial defect (1.5-3.0 cm in diameter) and suture the mitral valve dehiscence (0.8-1.8 cm), and the hearts resumed beating automatically after surgery. Autopsy: A female infant with complete AVSD combined with Ellis-van Creveld syndrome, 7 months, died of heart failure and pulmonary infection due to ineffective treatment, and Ellis-van Creveld syndrome with common atrium had been diagnosed before birth, which was confirmed by autopsy. Results Of the 21 children with AVSD in this group, 10 (47.6%) had partial AVSD and 11 (52.4%) had complete AVSD. The partial AVSD showed primary orifice atrial defect and mitral valve (anterior leaflet) cleft, one case combined with septal tumor formation, and one case with ectopic drainage of the left superior vena cava; among the complete AVSD, Rastelli’s staging: six cases of type A and three cases of type C, four of which showed single atrium, one case combined with oval orifice non-closure, one case combined with permanent arterial trunk, two cases combined with secondary orifice atrial defect, one case combined with complete Among them, 4 cases presented with single atrium, 1 case with oval foramen non-occlusion, 1 case with permanent arterial trunk, 2 cases with secondary foramen atrial defect, 1 case with complete pulmonary vein ectopic drainage, 2 cases with pulmonary valve stenosis, 1 case with left ventricular diverticulum, and 1 case with extracardiac malformation with trisomy 21, 1 case with no spleen syndrome and 1 case with Ellis-van Creveld syndrome. All of the children with complete AVSD were discharged automatically after conservative medical treatment due to their young age and severe disease. 5 children with partial AVSD underwent radical surgery under hypothermic extracorporeal circulation, and most of them had good postoperative follow-up, but only 1 case showed chronic heart failure 2 years after surgery, and ultrasound revealed different degrees of regurgitation in mitral, tricuspid, and pulmonary valves. The valve needs to be replaced. AVSD is a relatively rare congenital heart disease, accounting for 4-5% of congenital heart disease, and 2.9% of the recently reported cases, with a rate of 0.19 per 1,000 live births. In contrast, the proportion of congenital heart disease in our hospital statistics is 0.81%, which is relatively small. I. Nomenclature The name of this disease varies, some call it endocardial cushion defect, atrioventricular common channel, atrioventricular canal defect and atrioventricular joint defect, but atrioventricular septal defect is common, so today it is mostly called atrioventricular septal defect [1]. II. Pathological changes of AVSD The embryology of this disease is the abnormal development of the endocardial cushions, which forms its unique pathological changes, mainly including primary foramen atrial defect, subtricuspid ventricular defect and mitral and tricuspid leaflet fracture. In addition to the atrioventricular septum as the underlying lesion, the malformation of the atrioventricular valve is an important pathology, and the morphology of the valve leaflets, the retracted tendons and the papillary muscles are all malformed. In the normal fifth week the upper and lower endocardial cushions begin to join, dividing the common atrioventricular channel into two paths, if the upper and lower cushions fail to join, the downward development of the primary atrioventricular septum cannot join with the endocardial cushions, so a hole is left in the lower part of the primary septum called the primary foramen ovale, while in fact the development of the primary septum itself can be normal. The atrioventricular valve position is often low, the mitral and tricuspid valves are at the same level, while the aortic valve position is high, so the left ventricular outflow tract is long, forming the so-called gooseneck. The mitral valve is not well developed due to the endocardial cushion, resulting in the anterior valve being divided into two parts, leaving a cleft (the so-called mitral cleft). The site and size of AVSD shunts depend on the relationship between the bridging valve and the atrioventricular septum; if the bridging valve is attached to the crest of the ventricular septum, the shunt occurs at the atrial level; if the bridging valve is attached to the septum, the shunt occurs at the ventricular level; and if the bridging valve is suspended between the septum, the shunt occurs at the atrioventricular level. If the valve is suspended between the septum, the shunt occurs at the atrioventricular level. The disease is commonly associated with malformations such as tetralogy of Fallot, pulmonary valve stenosis, patent ductus arteriosus, secondary foramen ovale, trisomy 21, Ellis-van Creveld syndrome, etc. Complete AVSD (right type of heterogeneous isomerism) is often associated with no splenic syndrome, whereas complete AVSD (left type of heterogeneous isomerism) is occasionally associated with multiple splenic syndromes [1,2]; partial AVSD is often associated with DiGeorge’s syndrome [2]. With regard to chromosomal abnormalities, in addition to trisomy 21 (16% of cases) and the autosomal recessive Ellis-van Creveld syndrome described earlier, genetic disorders such as trisomy 18 and deletion of the long arm of chromosome 3p25 have been reported to be associated with the development of AVSD [4,5]. In our group of partial AVSD cases, one case was combined with septal aneurysm formation and one case was associated with ectopic drainage of the left superior vena cava; four cases of complete AVSD presented with single atrium, one case combined with patent foramen ovale, one case combined with permanent arterial trunk, two cases combined with secondary foramen atrial defect, one case combined with complete pulmonary vein ectopic drainage, two cases combined with pulmonary valve stenosis, one case combined with 21- trisomy, 1 case combined with no splenic syndrome, 1 case combined with Ellis-van Creveld syndrome, and 1 case combined with left ventricular diverticulum. Rastelli divided the complete AVSD into three types according to the deformity of the anterior bridging valve [1,2]. Type A: The anterior bridging valve is divided into two lobes of similar size, one in the right ventricle and one in the left ventricle, and its retracted tendons are connected to the associated anterior ventricular papillary muscle, while the central part has thin tendons connected to the crest of the septum or to the right ventricular septal surface beneath it, and the hole between the two ventricles is on the parietal crest of the septum, between the anterior and posterior bridging valves, and the septum has no exposed part of the valve. In this group of cases, there were 6 cases of type A, accounting for 54.5%, which was also the majority. Type B: The anterior bridge flap is divided into two parts, but the tendons in the middle are not directly implicated with the septum, but summed up to the papillary muscle of the right ventricular proximal septum, and the lateral flaps are still connected to the respective papillary muscle by the respective tendons. This type is less common because the anterior bridge flap is not associated with the septum and produces traffic between the two ventricles, and this type was not found in this group of cases. Type C: The anterior bridging valve is neither separate nor centrally attached to the septum or other parts of the ventricle, but floats above the septum, with both leaflets still attached to their respective ventricles. In this group of cases, there were 3 cases of type C, accounting for 14.2%. The clinical manifestations of AVSD are not different between male and female. Partial AVSD has mild clinical symptoms, such as small fractional flow and regurgitant flow, and can be asymptomatic in infancy and childhood, with high survival rate and good surgical results; while in complete AVSD, the symptoms appear early and heavy, and the symptoms of heart failure are more obvious, often accompanied by shortness of breath, feeding difficulties, occasional cyanosis, stunted growth, and early death, such as complete AVSD. If there is no heart failure, the presence of pulmonary hypertension or pulmonary artery stenosis should be investigated, in addition to the small amount of return flow. The mean age of partial AVSD was 6.1 years, while the mean age of complete AVSD was 4.37 months.