Refractory cardiac shock in the cardiac surgical intensive care unit confers significant morbidity and mortality. Extracorporeal membrane oxygenation (ECMO) has become a common intervention for refractory cardiogenic shock when other therapies have failed. However, it is difficult to predict who will benefit from this costly, resource-intensive, but potentially life-saving technology. Here, we discuss the utility of a novel biomarker, serum butylcholinesterase, in determining survival in patients supported with ECMO following cardiac surgery.