The authors studied the hemodynamic effects of rapidly weaning from mechanical ventilation (MV) 15 patients with severe chronic obstructive pulmonary disease (COPD) and cardiovascular disease who were recovering from acute cardiopulmonary decompensation. In each patient, 10 min of spontaneous ventilation (SV) with supplemental oxygen resulted in reducing the mean esophageal pressure (X +/- SD, + 5 +/- 3 to -2 +/- 2.5 mmHg, P less than .01) and increasing cardiac index (CI) 3.2 +/- 0.9 to 4.3 +/- 1.3 1/min/M2, P less than .001), systemic blood pressure (BP 77 +/- 12 to 90 +/- 11 mmHg, P less than .001), heart rate (HR 97 +/- 12 to 112 +/- 16 beats/min, P less than .001), and, most importantly, transmural pulmonary artery occlusion pressure markedly increased (PAOPtm 8 +/- 5 to 25 +/- 13 mmHg, P less than .001), mandating a reinstitution of MV. In four patients with left ventricular (LV) catheters, the PAOP correlated with the LV end-diastolic pressure during both MV and SV. Gated blood pool imaging showed SV increased the LV end-diastolic volume index (65 +/- 24 to 83 +/- 32/M2, P less than .002) with LV ejection fraction unchanged. Patients were treated for a mean of 10 days with diuretics, resulting in a reduction of blood volume (4.55 +/- 0.9 1 to 3.56 +/- 0.55 1) and body weight (-5 kg, P less than .001). Subsequently, nine of the 15 patients were weaned successfully from mechanical ventilation with unchanged PAOP.