Hysteroscopy is an established gynecologic procedure that has been used for the past 20 years as a diagnostic technique. It is also used therapeutically. Hysteroscopy is commonly performed with CO2insufflation and its complications are rare. The sudden decrease of end-tidal partial pressure of carbon dioxide, associated with mill-wheel murmur, loss of cardiac output and sinus tachycardia on the ECG are highly suggestive of massive gas embolism during laparoscopy and hysteroscopy. We report 2 cases of cardiac arrest and severe bradycardia. The second patient's expired CO2 concentration fell rapidly to 7 mmHg and blood pressure and heart rate dropped suddenly after resection of the uterine septum and adhesiolysis. We performed cardiac resuscitation with cardiotonic drugs, cardiac compression, defibrillator and resulted in good recovery. At the time of discharge 10 days and 2 days later, the patients had recovered almost completely.