Methemoglobinemia, an increased concentration of methemoglobin in the blood, is an altered state of hemoglobin whereby the ferrous form of iron is oxidized to the ferric state, rendering the heme moiety incapable of carrying oxygen. This can cause hypoxia, cyanosis, or even death. Severe methemoglobinemia resulting from oral benzocaine spray before endoscopic procedures has been reported as a rare complication. We report a case of severe acquired methemoglobinemia resulting from topical benzocaine use before transesophageal echocardiography. This case serves to highlight the severity of methemoglobinemia that can result from an otherwise innocuous agent even in small doses and the fact that prompt recognition and treatment of this disorder can be lifesaving.