Patients undergoing partial liquid ventilation (PLV) are often monitored with pulmonary artery catheters and receive positive end-expiratory pressure (PEEP). PEEP can dissociate wedge pressure (Pcw) from transmural left atrial pressure (Platm) by elevating pleural pressure and can dissociate Pcw from Pla by elevating alveolar pressure, PLV, like PEEP, also elevates pleural and alveolar pressures. However, the artifacts PLV may cause in measured vascular pressures are unknown. In 6 anesthetized, paralyzed healthy adult sheep, we compared effects of gas ventilation (GV) and PLV with 10 and 30 ml/kg perflubron on pericardial pressure (Pperi), Pcw, Pla, thermodilution cardiac output, and pulmonary artery flow measured with a doppler probe. PEEP was applied from 0-15 mm Hg during GV and PLV. PLV changed pericardial pressure or cardiac output minimally (at PEEP(0), GV: Pperi = -1.7 +/- 0.6 mm Hg, CO = 3. 2 +/- 0.1 L/m; 10 ml/kg perflubron: Pperi = -1.3 +/- 0.6 mm Hg, CO = 3.4 +/- 0.2 L/m; 30 ml/kg perflubron: Pperi = -1.6 +/- 0.7 mm Hg, CO = 3.4 +/- 0.2 L/m; all mean +/- SEM). On PEEP, Pcw agreed with Pla and Platm as well or better during PLV as during gas ventilation. Cardiac output by thermodilution and probe agreed equally well under all conditions. We conclude that hemodynamic values are as accurate during PLV as during gas ventilation.