Central venous pressure (CVP) recorded on electronic equipment (E-CVP) is compared with CVP measured by water column (W-CVP) in 50 patients after coronary bypass surgery without prior pulmonary symptoms. We find a statistically significant, but clinically insignificant, difference between E-CVP and W-CVP. Treatment with 10 cm H2O positive end expiratory pressure (PEEP) causes a significant rise in CVP by increasing intrathoracic pressure, but as changes in CVP rather than a given value are of greater importance in the daily clinical situation, we do not consider it clinically important to interrupt treatment with PEEP in as much as only small changes in CVP are induced after application of PEEP.