“…In other cases, it results from abnormal formation of patency of vascular connections, as, for example, pulmonary arterio-venous fistulas or less frequentlycollaterals between systemic veins and pulmonary veins or pulmonary venous atrium. 3,4,7,8 During the embryological development of the venous system, the involution of left cardinal vein occurs, resulting in an exclusively right-sided superior caval vein. However, in some subjects, the persistence of left superior caval vein occurs: in 0.3% of the population with normal cardiovascular system and in about 5% of the population with congenital cardiac anomalies.…”