We present the case of a 3-month-old girl who had unrepaired Tetralogy of Fallot who presented to the emergency department with an acute hypoxic episode. The patient was hyperpneic and cyanotic, with an initial oxygen saturation of 56%. She did not respond to knee-to-chest positioning. A single dose of intranasal fentanyl was administered with subsequent resolution of her symptoms and improvement of her oxygen saturation to 78% within 10 minutes. To our knowledge, this is the first report of the successful treatment of a hypoxic episode of Tetralogy of Fallot using intranasal fentanyl. Dr Tsze conceptualized the case report, wrote the manuscript, and critically reviewed and revised the manuscript; Dr Vitberg assisted with data acquisition and critically reviewed and revised the manuscript; Dr Berezow provided substantial intellectual input and critically reviewed and revised the manuscript; Dr Starc provided substantial intellectual input and critically reviewed and revised the manuscript; Dr Dayan provided substantial intellectual input and critically reviewed and revised the manuscript; and all authors approved the final manuscript as submitted.www.pediatrics.org/cgi