BACKGROUND Laparoscopic Nissen fundoplication (LNF) is gaining popularity. Although the hemodynamic effects of the typical pneumoperitoneum have been studied, the additional consequences of the hiatal dissection necessary for LNF have not. METHODS Seven female pigs were anesthetized, intubated, and ventilated with a volume ventilator and hemodynamic and mechanical pressure monitoring devices were placed. Pressures were recorded every 15 minutes for 1 hour after each of four interventions: (1) anesthesia induction, (2) CO2 pneumoperitoneum (15 mm Hg), (3) LNF, and (4) release of pneumoperitoneum (and removal of ports). RESULTS Right atrial, inferior vena caval, mediastinal, pleural, airway, and pulmonary capillary wedge pressures all increased after pneumoperitoneum (p < 0.05). Only mediastinal pressure (8.6 vs 13.7 mm Hg, pneumoperitoneum vs LNF; p < 0.05) and pleural pressure (2.6 vs 3.5 mm Hg, pneumoperitoneum vs LNF; p < 0.05) showed a further significant increase after LNF. In addition, cardiac output fell significantly after LNF (5.9 vs. 4.6 L/min; p < 0.05). Mediastinal pressure and cardiac output remained significantly altered after the release of pneumoperitoneum. CONCLUSIONS Surgical disruption of the esophageal hiatus during LNF causes both increased mediastinal and pleural pressure and a significant reduction in cardiac output. These findings uncover a previously unsuspected physiologic detriment that may occur during LNF.