Interposed abdominal compression CPR (IAC-CPR) has been demonstrated to significantly improve blood flow compared with standard (S)-CPR in animal and electrical models. Studies with IAC-CPR in human beings have not reported data regarding cardiac output. Animal and clinical studies have correlated end-tidal PCO2 (ETPCO2) with cardiac output produced with precordial compressions. We conducted a prospective, randomized study on 33 adult patients with nontraumatic cardiac arrest. Patients were randomized to initially receive either S-CPR or IAC-CPR. ETPCO2 was monitored continuously. After 20 minutes of resuscitation, the technique was reversed. The average ETPCO2 during IAC-CPR was 17.1 mm Hg while the average during S-CPR was 9.6 mm Hg, a difference of 78% (P less than .001). In patients arriving in cardiac arrest, return of spontaneous circulation was observed in six patients (30%) during IAC-CPR and in one patient (6%) during S-CPR (P = .07). Our study strongly suggests that cardiac output may be significantly increased in human beings with IAC-CPR as evidenced by the significantly greater increases in ETPCO2 with IAC-CPR compared with S-CPR. In addition, IAC-CPR appeared to demonstrate a trend toward increasing the return of spontaneous circulation.