The aim of this study was to examine the prognostic value of monitoring end-tidal carbon dioxide (ETCO2) levels for patients in cardiogenic shock undergoing percutaneous cardiopulmonary support (PCPS). Fifteen patients in whom PCPS was used to treat cardiogenic shock were enrolled in this study. For hemodynamic measurements, a thermodilution catheter was inserted into the pulmonary artery and an infrared absorption sensor was placed in the main stream of exhaled air between the respiration tube and the respirator to measure ETCO2 levels. Nine patients (group II, 60%) died of multiple organ failure. In the six survivors (group I), there was a significant increase in average ETCO2 level from 8.8 ± 3.9 mmHg before treatment to 20.5 ± 2.1 mmHg 24 h after the start of PCPS compared with values in group II patients (8.8 ± 3.9 mmHg, P = 0.0411). Also, serum lactate concentrations fell significantly in group I patients (group I 2.8 ± 0.47 mmol/l, group II 9.0 ± 2.31 mmol/l, P = 0.0435). The mean ETCO2 level in group I patients gradually returned to 23 mmHg, which was within the normal healthy range; these patients were successfully weaned from PCPS. These results suggest that, in cardiogenic shock patients, ETCO2 level is a possible index of cardiac recovery during PCPS support.