[citation needed] It is less severe than total anomalous pulmonary venous connection which is a life-threatening anomaly requiring emergent surgical correction, usually diagnosed in the first few days of life.

The severity of symptoms, and thus the likelihood of diagnosis, varies significantly depending on the amount of blood flow through the anomalous connections.

In less severe cases, with smaller amounts of blood flow, diagnosis may be delayed until adulthood, when it can be confused with other causes of pulmonary hypertension.

[9][10] However, interest is increasing in catheter-based interventional approaches, as well as medical therapy for less severe cases[citation needed].

To understand the different types of anomalous pulmonary venous connection, it is important to establish the background in which normal fetal vasculature develops.