Acute toxic methemoglobinemia is an infrequent complication of the use of topical anesthetics, most notably benzocaine. The clinical picture is characterized by sudden development of tissue hypoxia without underlying cardiac or respiratory dysfunction, and deceptively normal oxygen saturation on conventional arterial blood gas analysis. This condition may be rapidly fatal and management depends upon prompt recognition, confirmation of clinical suspicion using cooximetry of arterial blood, and quick institution of therapy. We describe the first reported case of cardio-respiratory failure associated with acute toxic methemoglobinemia, which was initially misconstrued as an evolving acute coronary event and rapidly responded to methylene blue therapy.