Respiratory failure in myxedema is a complex medical emergency and may require prolonged ventilatory assistance. Chronic hypothyroidism is easily neglected by clinician due to the lack of specific symptoms and signs. It is also easily misdiagnosed as heart failure. We report a 55-year-old woman with chronic hypothyroidism. She had been treated for congestive heart failure for years. Myxedematous coma was not diagnosed until respiratory failure occurred. After replacement with levothyroxine, she was successfully weaned from prolonged mechanical ventilation.