The effects of incremental positive end-expiratory pressure (PEEP) on right ventricular RV) function were evaluated in 36 (n = 36) ventilated patients. Positive end-expiratory pressure was increased from 0 (baseline) to 20 cm H2O in 5-cm H2O increments and RV hemodynamics and thermally derived right ventricular ejection fraction (RVEF), right ventricular end-diastolic volume index (RVEDVI), and right ventricular end-systolic volume index (RVESVI) were computed. Right ventricular contractility was determined from the analysis of RV systolic pressure-volume relations. Right ventricular ejection fraction declined from 42 ± 8% at baseline to 30 ± 9% at 20 cm H2O PEEP. Right ventricular end-diastolic volume index declined between 0 and 5 cm H2O PEEP (103 ± 42 to 92 ± 34 ml·m−2) and then increased to 113 ± 40 at 20 cm H2O PEEP. Right ventricular end-systolic volume index increased from 60 ± 31 ml·m−2 at baseline to 79 ± 34 ml·m−2 at 20 cm H2O PEEP. The slope (E) of the relation of RV peak systolic pressure to RV end-systolic volume index decreased from 0.26 mm Hg·m2·ml−1 between PEEP of 0–15 cm H2O to 0.05 mm Hg·m2·m−1 at PEEP > 15 cm H2O. It is concluded that low levels of PEEP have a predominant preload reducing effect on the RV. Above 15 cm H2O PEEP, RV volumes increase and E decreases, consistent with increased RV after load and a decline in RV contractility.