A triple atrium heart is a relatively rare congenital heart malformation, accounting for 0.1%-0.4% of congenital heart disease, with a male to female ratio of 1.5:1. A triple atrium heart can be divided into a left type and a right type, with the left atrium being separated by an abnormal muscle fiber septum into a secondary atrium and a true left atrium called a left triple atrium heart, and the right atrium being separated by an abnormal muscle fiber septum into a secondary atrium and a true right atrium called a right triple atrium heart. The term triatrial heart is usually used to refer to the left triatrial heart. During embryonic development, the pulmonary vein common trunk is abnormally connected to the left atrium and fails to fuse into one, and the left atrium is separated into two chambers, forming a triple atrium heart. The natural regression of the triatrial heart depends mainly on the size of the traffic orifice between the paratria and the true atria. If there is no traffic or if the foramen ovale is small, the prognosis is similar to that of a complete pulmonary vein drainage, with severe symptoms soon after birth and death in infancy in about 75% of cases without surgical treatment. If the traffic orifice is large or combined with an atrial septal defect, the natural prognosis is better, with symptoms appearing in childhood and early adulthood. Patient symptoms, signs and prognosis are similar to those of partial pulmonary vein ectopic drainage and mitral stenosis.