Shock and coma developed suddenly in a 54-year-old male undergoing irrigation of an infected and fistulous herniorrhaphy wound with 3% hydrogen peroxide (H2O2). Marked ST elevation was seen in almost all electrocardiogram (ECG) leads. Within one hour the patient recovered completely, and the ECG returned to normal. The mechanism of this occurrence was most likely widespread embolization of oxygen microbubbles released from absorbed H2O2. The danger of hydrogen peroxide irrigation in closed spaces is emphasized.