Commonly identified risk factors for perioperative cardiac arrest in pediatric-aged patients include cardiac surgery, younger age, comorbid conditions including pulmonary hypertension and cyanotic congenital heart disease, and emergency surgery. Although medication-related etiologies formerly predominated, the elimination of halothane from anesthetic care has resulted in a shift in etiology to hemodynamic events related to blood loss or hyperkalemia associated with the rapid administration of blood products. Rarely, cardiac arrest can be sudden and unexpected without an identified pre-existing etiology in an otherwise apparently healthy patient. We present an 18-year-old adolescent who experienced pulseless electrical activity (PEA) and cardiac arrest following anesthetic care for an outpatient orthopedic procedure, who was eventually diagnosed with hypothyroidism. The potential etiologies of PEA and cardiac arrest during anesthesia are reviewed, components of successful resuscitation discussed, and an outline for the investigative workup presented.