The squatting phenomenon is a specific type of forced body position, mostly seen in children with precocious tetralogy of Fallot. So, what are the differential diagnoses for him? The following is the differential diagnosis of squatting phenomenon: 1. Pulmonary artery orifice stenosis combined with atrial septal defect with right-to-left shunt (tetralogy of Fallot) The cyanosis appears later in this disease. The systolic murmur at the second intercostal space on the left edge of the sternum is louder and occupies a longer period of time, and the second heart sound in the pulmonary valve area is reduced and split. a more significant enlargement of the heart shadow is seen on X-ray, and the arc of the common pulmonary artery trunk is significantly protruding. Right ventricular strain was more pronounced in the electrocardiogram. The diagnosis can be established by right heart catheterization, selective indicator dilution curve determination or selective cardiovascular angiography, which reveals a valvular type of pulmonary artery orifice stenosis with right-to-left shunt level at the atrial site. 2. Eisenmenger syndrome When severe pulmonary hypertension occurs in patients with ventricular septal defect, atrial septal defect, aorto-pulmonary septal defect or arterial catheterization, the left-to-right shunt is converted into a right-to-left shunt, forming Eisenmenger syndrome. In this syndrome, cyanosis appears late, and X-ray examination shows that the arc of the common trunk of the pulmonary artery is obviously protruding, and the vascular shadow of the pulmonary hilar is coarse while the vascular shadow of the pulmonary field is small; right heart catheterization reveals significant pulmonary artery hypertension, etc., which can be distinguished. In Ebstein malformation and tricuspid atresia, the septal and posterior leaflets of the tricuspid valve are shifted down to the ventricle, and the right atrium is enlarged while the right ventricle is relatively small, often accompanied by an atrial septal defect that causes right-to-left shunt. Four heart sounds can be heard in the precordial region; X-ray shows enlarged heart shadow, often spherical, and the right atrium can be very large; electrocardiogram shows right atrial hypertrophy and right bundle branch conduction block; selective right atrial angiography shows enlarged right atrium and malformed tricuspid valve, which can establish the diagnosis. 4.Large vessel misalignment In complete large vessel misalignment, the pulmonary artery originates from the left ventricle, while the aortic origin is from the right ventricle, often accompanied by atrial or ventricular septal defect or ductus arteriosus, the heart is often significantly enlarged, and the X-ray shows pulmonary congestion. 5.Immortal arterial trunk There is only one set of semilunar valves in the immortal arterial trunk, which spans over the two ventricles, from which the pulmonary artery and cephalic brachial artery emanate.