OBJECTIVE We report a case of massive air embolism in the cardiopulmonary bypass (CPB) circuit to highlight the principle of its immediate management and its preventive measures. METHODS The air embolism was caused by the accidental connection of carbon dioxide (CO(2)) supply to the monitoring arm of the retrograde cardioplegia delivery system. The CPB ceased, resulting in cardiac arrest requiring immediate internal cardiac massage. Cerebral protective measures were also instituted instantaneously and the air embolism was purged from the CPB circuit. The cause of air embolism was identified after high initial arterial CO(2) concentration was detected in the blood gas analysis. The CO(2) supply was disconnected, and CPB was restarted. Spontaneous cardiac activities resumed shortly after, and the operation was completed uneventfully. RESULTS The patient had no immediate post-operative sequel and remained well at 6 weeks follow-up. CONCLUSIONS Massive air embolism in cardiopulmonary bypass (CPB) circuit is a life-threatening emergency. Immediate cerebral protective manoeuvres and rectification of the cause of air embolism are vital for favourable outcome. However, high degree of vigilance and cooperation amongst all teams involved are paramount to prevent its occurrence in the first place.