This technique article describes a novel method for converting pediatric patients from veno-arterial extracorporeal membrane oxygenation (VA-ECMO) to cardiopulmonary bypass (CPB) using a single circuit with the addition of a cardiotomy reservoir. In seven patients (eight procedures), the approach preserved circulating blood volume, limited donor exposure, and maintained effective surgical support. All patients were successfully decannulated, demonstrating feasibility and safety in complex congenital heart surgery.