In four postoperative cardiac patients during controlled ventilation, acute circulatory failure was associated with decreases in end-tidal CO2(Petco2) and cardiac index. Closed cardiac compression caused an increase in both Petco2and cardiac index, with complete restoration to baseline values after successful CPR. Our data indicate that Petco2measurements during controlled ventilation in acute circulatory failure patients may be used as an indirect noninvasive tool to monitor the patient's hemodynamic status during CPR.