Abnormal systemic venous connections are usually of little surgical significance, since their clinical consequences are limited, although in the severest form, totally anomalous connection, the changes can be profound. Fortunately, totally anomalous systemic venous connection is very rare. The less severe variants are more likely to be encountered as the surgeon pursues a more complex associated intracardiac anomaly, such as the sinus venosus interatrial communication. The anomalous connections in general are of most significance in the setting of isomeric atrial appendages, which we discuss in Chapter 11, emphasizing how so-called visceral heterotaxy is best considered in terms of right versus left isomerism. In this chapter, we consider the features of the anomalous systemic venous connections in their own right. They may be grouped into the categories of absence or abnormal drainage of the right caval veins, persistence or abnormal drainage of the left caval vein, abnormal hepatic venous connections, and totally anomalous systemic venous connections.