Atrial Septal Defect (ASD) is the most common congenital disorder found in adulthood, accounting for 35% of Adult Congenital Heart Disease (ACHD). In ASD, there is a defect in the septum/wall between right and left atria, resulting in left-to-right shunt which lead to an increase of the right heart volume and pulmonary circulation. If left untreated, increased pulmonary resistance develop to pulmonary hypertension (PH) which results in a progressive decrease in right ventricular function, causing right heart failure and death. Although ASD surgical closure is not a complicated procedure, patients with complication of PH and right heart failure have a high mortality rate if not managed properly. Increase in mortality was mainly due to perioperative pulmonary hypertensive crisis (PH crisis), condition of an acute increase in mean pulmonary arterial pressure (mPAP) exceeding mean systemic arterial pressure (MAP). In this case report, we will discuss the management of postoperative adult patients with ASD closure complicated by intraoperative pulmonary hypertensive crisis who are treated in the intensive care unit (ICU).