This consist of a large left (L) to right (R) shunt, which causes severe pulmonary (lung) vascular disease and high blood pressure (in the lungs) with resulting reversal of the direction of shunting (figure 23F). This shunting with increase pressure causes the lung arteries to narrow due to thickening of their walls (especially the middle wall, called tunica media, see figure 23F) and cause obstruction. Initially the changes may be reversible, but ultimately they become irreversible due to inflammation of the arteries. Hence, much of the lung arteries are occluded, leading to increase pulmonary blood vessel resistance. Ultimately the resistance in the lungs may exceed the resistance in the arteries of the rest of the body, which leads to a reversal of flow from left-to-right to right-to-left shunt.

The reversal of the shunt leads to cyanosis, as well as shortness of breath, coughing up blood, reduced exercise tolerance, syncope (fainting), palpitations, and atrial fibrillation (see figures 15A, B). Brain events such paradoxical embolus, thrombosis (stroke) and hemorrhage may occur. Heart failure suggest a poor prognosis, and sudden death is possible.

Digital swelling (clubbing) may occur. Heart murmurs may occur .

EKG may show RVH and atrial arrhythmias (see figures 2, 3a, 3b, 5a, 5b, 14, 15a, 15b).

Echocardiogram shows RV pressure overload, pulmonary high blood pressure, and the underlying heart defect. Using intravenous contrast injections along with echocardiogram will visualize the intracardiac defect.Heart catherterization is necessary to assess the lung hypertension and the size of the defect.

Rate of survival is 80% 10 years after diagnosis, 77% at 15 years, and 42% at 25 years. Death is usually sudden, presumably due to arrhythmias, but some die of the above mentioned complications.

Lung transplantation with repair of the cardiac or combined heart-lung transplantation is an option for patients with a poor prognosis (failing to respond to medical therapy).