Total anomalous pulmonary venous connection (TAPVC) has been classified into four types by Craig JM, Darling RC and Rothney WB in 1957 . It is popularly known as Darling classification. According to this classification, TAPVC is divided into four types based on the anatomic site of the anomalous connection. Type 1 is a supracardiac, type 2 is an intracardiac, type 3 is infracardiac and type 4 a mixed variety. This is the most commonly used classification.
In the supracardiac variety, the four pulmonary veins drain into a common venous chamber which drains to the left brachiocephalic vein through a vertical vein. In type 2, the pulmonary veins drain to the coronary sinus or directly into the right atrium. In type 3, the pulmonary veins connect to a vertical vein which drains below the diaphragm, either into the portal vein or its branches. Type 4 or mixed type is usually a combination of types 1 and 3 . The commonest variety is the supracardiac or type 1, which constitutes about half the number of cases. Types 2 and 3 are almost equally seen in about one fifth of cases and type 4 in about one tenth of the cases.
Another simple classification has been proposed by Smith B et al, which simply divides TAPVC into 2 groups . They are supradiaphragmatic without pulmonary venous obstruction and infradiaphragmatic with pulmonary venous obstruction .
Several other classifications have been published like a detailed classification by Herlong JR et al  and a classification of the mixed type by Chowdhury UK et al .