Positive end-expiratory pressure (PEEP) may decrease venous air embolism (VAE) by increasing venous pressure at the incision level. Because PEEP and VAE can both increase pulmonary vascular resistance, it is possible that the application of PEEP during VAE may increase right atrial pressure (RAP) relative to left atrial pressure (LAP) and thereby reverse the normal interatrial pressure gradient, allowing paradoxical air embolism in patients with a probe-patent foramen ovale. We studied atrial pressures during 0, 4, and 8 mmHg PEEP before and during continuous VAE in both supine and upright tilted dogs. Both PEEP and VAE increased pulmonary artery pressure and resistance. Prior to VAE, PEEP increased both RAP and LAP but did not affect the interatrial pressure gradient. VAE alone did not affect RAP, LAP, or the interatrial pressure gradient. Application of PEEP during VAE had similar effects as at baseline, namely an increase in RAP and LAP with no change in the interatrial pressure gradient. Although RAP exceeded LAP more frequently in the upright than in the supine dogs, the effects of PEEP and VAE on atrial pressures were similar in both groups. Our finding that PEEP and VAE did not disproportionately increase RAP compared with LAP is consistent with other studies demonstrating preservation of right ventricular function in situations of increased right ventricular afterload.