The change of blood gases, hemodynamics and oxygen delivery after weaning and the treatment of sodium nitroprusside were respectively studied in seven and twelve patients with cor pulmonale. Weaning resulted in decrement of pulmonary vascular resistance (from 48.4 +/- 16.6 to 37.6 +/- 18.5 kPa.s-1.L-1, P < 0.01) and increment of oxygen pressure of mixed venous blood (from 5.35 +/- 0.71 to 6.00 +/- 0.89 kPa.s-1.L-1, P < 0.01). Although artery pressure of oxygen (from 12.20 +/- 4.24 to 10.07 +/- 2.83 kPa, P < 0.01) was decreased after the treatment of sodium nitroprusside, cardiac index (from 44.5 +/- 10.3 to 53.0 +/- 13.7 ml.s-1.m-2, P < 0.05) and oxygen delivery index (from 7.9 +/- 1.6 to 9.3 +/- 2.2 ml.s-1.m-2, P < 0.05) were improved. It indicates that adequate weaning and application of vasodilator is useful to mechanically ventilated patients.