Clinical reports on unintentional mass exposure to extreme concentrations of carbon dioxide are rare. We describe an industrial incident caused by a container of liquid carbon dioxide that was unintentionally opened in an enclosed working environment. Twenty-five casualties reached our emergency department. Symptoms included dyspnea, cough, dizziness, chest pain, and headache. ECGs (n=15) revealed ST-segment changes in 2 (13.3%) patients, atrial fibrillation in 2 patients, and non-Q wave myocardial infarction in 1 patient. Chest radiographs (n=22) revealed diffuse or patchy alveolar patterns, consistent with pneumonitis, in 6 (27%) patients and pulmonary edema in 2 (9%) patients. Eleven (44%) patients were admitted to the hospital: 8 were discharged 24 hours later and the others within 8 days. No patient died. Exposure to high concentrations of carbon dioxide resulted in significant but transient cardiopulmonary morbidity with no mortality when victims were promptly evacuated and given supportive therapy. Cardiac complications were frequently observed and should be actively sought.