Bilateral phrenic nerve palsy associated with open-heart surgery. The incidence of phrenic nerve palsy after open-heart surgery has been estimated at 10%, but it is usually unilateral and does not cause symptoms. Bilateral phrenic nerve injury after coronary artery bypass surgery is a rare complication. This case report describes a patient who developed bilateral phrenic nerve palsies and required prolonged ventilatory support. Denervation of both hemidiaphragms was documented by needle electromyography four weeks after bypass surgery. The patient required total ventilatory support for three months and partial ventilatory support for an additional three months. This case demonstrates the usefulness of electromyographic screening for documentation and prognostication after phrenic nerve injury. The cause of the lesion was unclear, but hypothermia and stretch were leading hypotheses. This patient developed the phrenic nerve palsies despite using a cardiac insulation pad. 