A 46-year-old man underwent angioplasty of a restenotic bifurcation lesion of the circumflex artery. The procedure required repeated balloon exchanges and during the last balloon inflation, no balloon was visualized. A test injection revealed a massive coronary air embolism due to expulsion of air that had accumulated in the guiding catheter shaft. The patient was rapidly resuscitated from electromechanical dissociation with intracoronary injection of adrenaline and atropine and forceful intracoronary saline injections. Inspection of the balloon revealed a defect and scratch marks at the junction of the wire part and shaft of the monorail balloon, a location that places the air leakage inside the guiding catheter. This is the first report of massive intracoronary air embolism due to an undetectable damage to the shaft of a balloon angioplasty catheter. Recognition of the problem and immediate intervention is vital in limiting the duration of cardiac dysfunction.