We assessed the effect of pressure support ventilation (PSV) on breathing patterns and the work of breathing in 10 postoperative patients. Minute ventilation (VE) increased by 8% with 5 cm H2O PSV and 10% with 10 cm H2O PSV compared to 0 cm H2O PSV. The increase in VE was achieved by increased mean inspiratory flow (24% with 5 cm H2O PSV and 67% with 10 cm H2O PSV) and a decrease in duty cycle (13% with 5 cm H2O PSV and 39% with 10 cm H2O PSV). The decrease in duty cycle along with a decrease in respiratory frequency allowed a greater expiratory time including a rest period for the respiratory muscles, which might minimize the risk of muscle fatigue. Furthermore, the inspiratory work added by the ventilator was near zero with 5 cm H2O PSV and 10 cm H2O PSV. Oxygen consumption also decreased significantly with 5 cm H2O PSV. We conclude that PSV improves the breathing patterns and minimizes the work of breathing spontaneously via a ventilator.