Triatrial heart is a congenital cardiovascular malformation in which the left atrium or right atrium is divided into two parts by a fibromuscular septum due to embryonic development disorder. It is a rare congenital heart disease, accounting for about 0.1% of congenital heart diseases. The triatrial heart usually refers to the left atrium being divided into the accessory atrium and the true left atrium (connected to the left atrial appendage and communicating with the left ventricle through the mitral valve). Dextrocardia is rare, accounting for only about 8% of triatrial heart cases. There are many types of triatrial heart classifications, which can be divided into three types: a, b, and c according to the location of the accessory atrium: type a, the accessory atrium is located above the true left atrium; type b, the accessory atrium is located on the inner and posterior side of the true left atrium; type c, the accessory atrium straddles the atrial septum. From the perspective of hemodynamics, it is roughly divided into two types: mitral stenosis type and atrial septal defect type according to the communication between the accessory atrium and the true left atrium, and the communication between the left and right atria.