Atrial septal aneurysm (ASA) formation is due to a deformity at the fossa ovalis. While previously considered a rare cardiac anomaly found postmortem, it can now be diagnosed at the bedside with ultrasound. Unrepaired ASA can lead to right-sided heart failure and pulmonary hypertension. The case we describe is complicated by the patient’s code status, limiting our ability to perform potential life-sustaining interventions. We also encountered a complication of rebound pulmonary hypertension with the use of inhaled nitric oxide. We detail the critical course of profound hemodynamic and respiratory instability responsive to salvage therapy.