A large population of patients with congenital heart disease with relevant systemic to pulmonary shunts( left to right shunts) will develop pulmonary arterial hypertension if left untreated. There are 2 different statuses of an increase in pulmonary arterial pressure. One is high resistance due to high pulmonary blood flow( high flow with high resistance), another one is low pulmonary flow due to high resistance( low flow with high resistance). Chronic large left-to-right shunt induced severe pulmonary vascular disease and pulmonary hypertension. This was then subsequence of low pulmonary blood flow with high pulmonary vascular resistance. We have to avoid this situation and have to do intervention while the pulmonary vascular reactivity has been left. Therefore accurate diagnosis, preoperative treatment for avoidance of high flow, appropriate timing of interventions and post operative various managements are important factors as aiming of low pulmonary resistance in this group. It is important to be familiar with.