A novel pressure gated tidal flow extracorporeal circulation (TF ECC) device was developed, and it was hypothesized that it could provide total respiratory support in apneic adult sheep without adverse hemodynamic or cardiac effects. The circuit consisted of a single lumen cannula, computer driven tubing occluders gated by circuit pressure, a nonocclusive peristaltic blood pump, a spiral coiled membrane lung, and a heat exchanger. Six paralyzed, anesthetized adult sheep were instrumented and TF ECC was instituted via cannulation of the right atrium. Total respiratory support was provided by the circuit during an apneic period of 6 hours. Echocardiography was performed with the animal instrumented (baseline) and after 2 hours of TF ECC. Circuit blood tidal volume was 172.6 +/- 18.0 cc, resulting in a TF ECC flow of 71.1 +/- 10.1 cc/kg/min. At the end of the study period, PaCO2 was 35.5 +/- 7.6 mmHg, paO2) was 91.2 +/- 30.6 mmHg, and pulmonary artery oxygen saturation (SPAO2) was 95 +/- 5%. Hemodynamic stability was maintained with no significant differences at baseline and after 6 hours in mean arterial pressure, mean pulmonary artery pressure, or heart rate noted. Echocardiographic evaluation showed preserved fractional shortening of the left ventricular (LV) septal-lateral dimension (baseline 32.4 +/- 11.4%; 2 hours 34.8 +/- 8.4%). This study demonstrates TF ECC provides total respiratory support without adverse hemodynamic effects, and preserved LV function.