This case report describes the successful use of an intraoperative modified Valsalva maneuver to reverse atrial flutter in a pediatric patient with complex congenital heart disease undergoing systemic-to-pulmonary shunt surgery. The technique involved manipulating the Adjustable Pressure Limiting (APL) valve on the anesthesia machine to simulate the hemodynamic effects of the modified Valsalva maneuver, allowing for non-invasive management of supraventricular tachycardia without pharmacological intervention or electrical cardioversion. This intervention stabilized the patient's arrhythmia, maintaining hemodynamic stability throughout the procedure. The case highlights the potential of the maneuver as a safe, effective, and non-invasive alternative for arrhythmia management in pediatric cardiac surgeries, advocating for further research to validate this approach and possibly integrate it into standard practice for similar clinical scenarios.