Massive air embolism during cardiopulmonary bypass is one of the most serious complications in open heart surgery. We report such an accident, which was managed by temporary retrograde perfusion through the superior vena cava. A 59-year-old woman with severe mitral stenosis underwent mitral valve replacement. Soon after the start of the bypass, a massive air embolism occurred, probably because a bend in the tubing caused the blood level in the oxygenator to fall. The pump was stopped immediately and the patient was placed in the deep Trendelenburg position. The pump circuit was primed rapidly with fluid and retrograde perfusion through the superior vena cava was done at a flow rate of 1.5 L/min for 5 min. After air return from the aortotomy was confirmed, the standard bypass procedure was resumed with hypothermia. When the accident was discovered, and until the end of the operation, deep anesthesia was induced with pentobarbital for protection of the brain. Mitral valve replacement and tricuspid annuoplasty were done in the usual way thereafter. Postoperatively, the patient had no neurologic sequelae except for transient generalized convulsions, and has returned to normal daily activities.