Dumping syndrome is a rare but potentially serious condition that causes inappropriate postprandial hyperinsulinemia leading to hypoglycemia in children following gastrointestinal surgeries. While dietary modifications are often the first line of treatment, severe cases may require pharmacological intervention to prevent severe hypoglycemia. We present a case of successful treatment of dumping syndrome with diazoxide. A 2-month-old infant with left hypoplastic heart syndrome who underwent single ventricle palliation pathway and developed feeding intolerance that required Nissen fundoplication. Postprandial hypoglycemia was detected following the procedure, with glucose level down to 12 mg/dL, and the diagnosis of dumping syndrome was established. The patient was successfully managed with diazoxide, which effectively resolved postprandial hypoglycemia without any major adverse events. The patient was eventfully weaned off the medication at the age of 5 months. This case highlights the potential role of diazoxide in the management of pediatric patients with postprandial hyperinsulinemic hypoglycemia secondary to dumping syndrome. Dumping syndrome is a possible complication of gastrointestinal surgeries and should be suspected in children with abnormal glucose levels. Postprandial hyperglycemia should be monitored closely for significant subsequent hypoglycemia. Diazoxide might be considered as part of the treatment plan for dumping syndrome.