The normal human heart is divided into the left and right atria and the left and right ventricles, which are separated from each other by a layer of tissue called the septum. If an abnormality occurs during the development, resorption, or fusion of the original atrial septum during fetal heart development, an unclosed atrial hole remains between the left and right atria, called an atrial septal defect. Atrial septal defects are divided into primary and secondary septal defects, with the latter being more common. It can exist alone or in combination with other cardiovascular malformations. What are the clinical manifestations of atrial septal defect? The symptoms of secondary foramen ovale septal defects are inconsistent. They are related to the size of the defect and the amount of fractional flow. Patients with large defects present early with symptoms, while patients with small defects may remain asymptomatic for a long time until old age. Most patients are asymptomatic in childhood and are often detected during physical examinations, and symptoms usually appear after young adulthood, mostly between the ages of 21 and 40. The main symptoms are palpitations and shortness of breath after activity and symptoms of respiratory infections such as cough. Pediatric cases are prone to recurrent severe lung infections due to lung congestion. It manifests as excessive cough and shortness of breath. Due to the reduction of left heart blood flow, patients tend to have lack of physical strength, easy idleness and dyspnea, and are more likely to feel shortness of breath and palpitations after activities. The prolonged increase in right heart load can be followed by pulmonary hypertension and right heart failure, and the patient’s symptoms worsen at this stage. Post-activity syncope, right heart failure, hemoptysis, cyanosis, etc. may occur and develop into Eisenmenger’s syndrome. The enlargement of the right ventricle increases with age, causing the adjacent thorax to appear enlarged and full. A systolic murmur with a hyperactive second heart sound and splitting is heard between the second and third intercostal spaces on the left side of the sternum near the sternum, which is important for diagnosis. X-rays indicate pulmonary congestion and enlargement of the right atrium and ventricle, and electrocardiograms often indicate a right-sided electrical axis. What is the natural course of atrial septal defect? The overall natural closure rate of atrial septal secondary foramen ovale defects is 87%. Atrial septal defects diagnosed before 3 months of age with a defect <3 mm close spontaneously in 100% of cases within 1.5 years of age; atrial septal defects with a defect between 3 and 8 mm close spontaneously in more than 80% of cases within 1.5 years of age; and defects above 8 mm rarely close spontaneously. The most basic hemodynamic change in atrial septal defects is a left-to-right shunt at the atrial level. The shunt flow varies depending on the size of the defect and the pressure difference between the two chambers. The pathological process can be divided into three stages. 1, because the pulmonary circulation can accommodate a large amount of blood, even if the blood volume of the pulmonary circulation has been two to three times that of the body circulation, it can still only hold the normal pulmonary artery pressure, so the vast majority of patients have no symptoms at this stage, and their activity does not decrease, only showing slower growth and susceptibility to respiratory infections. 2, a long time a large number of left to right shunt, small pulmonary arteries gradually produce intimal hyperplasia and middle layer hypertrophy, the formation of pulmonary hypertension, the right heart burden gradually increased. Therefore, the patient's symptoms are usually obvious gradually after young age, and symptoms such as panic and shortness of breath after activity, easy fatigue and cough can appear. 3. If the lesion is not corrected in time, the pulmonary artery pressure becomes higher and higher, the right heart burden gradually increases, and right-to-left shunt can appear at the atrial level. At this stage, the patient's symptoms worsen, and post-activity syncope, right heart failure, hemoptysis, cyanosis, and development of Eisenmenger syndrome may occur. Most children with atrial septal defects are generally asymptomatic and inactive, but heart failure can occur in infants, but is very rare. If left untreated, congestive heart failure and pulmonary hypertension will occur in adults in their 20s or 30s. Infective endocarditis does not occur in simple atrial septal defects, so prophylactic treatment is not necessary if there are no other co-morbidities. Cerebrovascular accidents, due to cerebrovascular embolism caused by atrial septal defect, are a relatively rare complication. How to diagnose atrial septal defect? 1.X-ray: increased pulmonary vascular shadow, bulging and enhanced pulsation of pulmonary artery trunk, enlarged right atrium and right ventricle, reduced aortic node, primary foramen ovale defect may have enlarged left ventricle. 2.Electrocardiogram: often combined with incomplete or complete right bundle branch conduction block, right ventricular hypertrophy. 3.Echocardiography: widening of the pulmonary artery, enlargement of the right atrium and right ventricle, and continuous interruption of the atrial septum. Abnormal shunts were seen on acoustic imaging. Echo Doppler; systolic left-to-right shunt spectrum can be measured in the right side of the atrial septum. 4. Cardiac catheterization: right heart catheterization reveals that the oxygen content of the right atrium is higher than that of the superior vena cava by 1,9% volume. 70% of cases, the cardiac catheter can enter the left atrium from the right atrium through the defect. The right heart catheter allows measurement of pressure at each site and calculation of fractional flow. Cardiovascular angiography may be considered if there is a suspected primary orifice defect, narrowing of the pulmonary artery orifice, or abnormal pulmonary venous drainage and other abnormalities. How is an atrial septal defect treated? All atrial septal defects should be treated surgically once diagnosed. A few small atrial septal defects can close on their own before the age of 1 year. Most scholars believe that as soon as the diagnosis is clear, surgery should be performed to abort the left-to-right shunt in time to avoid pulmonary hypertension and subacute bacterial endocarditis. The age of surgery is 5 to 12 years, but early surgery is recommended for patients with large defects who have congestive heart failure in early childhood, regardless of age. Currently, most of the surgical procedures are performed under extracorporeal circulation with direct visualization. Depending on the size and location of the defect, direct suture or patch repair is used during surgery. The surgical results of secondary foramen defects are positive, and most patients have disappeared after surgery and can participate in work and study. The mortality rate is generally below 2%. The cause of death is mainly directly related to age, history of heart failure and degree of pulmonary hypertension. The success rate of surgery for primary foramen ovale septal defect simple type or partial type is also high with good results, and the mortality rate is around 5 or 6%. The main causes of death are related to the patient's age, heart size, cardiac function and degree of lesion.