| A. Eisenmenger syndrome |
| Includes all systemic-to-pulmonary shunts due to large defects leading to a severe increase in PVR and a reversed (pulmonary-to-systemic) or bidirectional shunt. Cyanosis, erythrocytosis, and multiple organ involvement are present |
| B. PAH associated with systemic-to-pulmonary shunts |
| Patients with moderate-to-large defects, in which the increase in PVR is mild-to-moderate, left-to-right shunt is still largely present and no cyanosis is present at rest |
| C. PAH with small defects |
| Patients with a clinical picture very similar to idiopathic PAH, who have (coincidental?) small cardiac defects: a ventricular septal defect <1 cm and an atrial septal defect <2 cm |
| D. PAH after corrective cardiac surgery |
| Congenital heart disease has been corrected but PAH is still present immediately after surgery, or has recurred several months or years after surgery in the absence of significant post-operative residual congenital lesions or defects that originate as sequelae of previous surgery |
PVR: pulmonary vascular resistance. Reproduced with modification from [2].