The natural history of untreated patients of TAPVC is not very favorable. It depends on the type of obstruction and amount of shunting across the atrium.

The natural history of untreated patients of total anomalous pulmonary venous connection depends on:

• Type of obstruction (unobstructed, obstructed)
• Type of anatomic variant(cardiac, infracardiac or supracardiac)
• Amount of right-to-left shunting

Untreated patients:^[1]

• Patients with severe obstruction may not be able to survive beyond few months of life.
• 8 out of 10 patients with small interatrial connections and obstruction die as an infant.
• The presentation of patients with unobstructed TAPVC and large interatrial shunting may vary from asymptomatic to symptoms due to progressive right heart failure.

Complications of TAPVC include:

• Breathing difficulties
• Dysrhythmias
• Pulmonary infections
• Heart failure

Long-term complications include:

• Dysrhythmias
• Pulmonary hypertension

Prognosis of total anomalous pulmonary venous depends on whether the surgery has been done with the patient. Without surgery, death may occur by age one in babies with more severe defects.