With changes in heart rate and mean aortic pressure, an intraaortic balloon (IAB) works with incomplete inflation. The effects of initial peak positive pressure and plateau holding positive pressure on IAB volume were investigated and minimum pressures necessary to inflate an IAB to a desired volume were established with a standard IAB catheter (Datascope type, 9.5 Fr, 40 ml). Initial peak pressure greater than 200 mm Hg was adequate to attain the desired volume of the IAB. Plateau positive pressure should be altered in accordance with hemodynamic changes.