Background: About 27% of the population is known to have a patent foramen ovale. It can be opened if the left atrial pressure is less than the right atrial pressure. This pressure reversal has been reported during gynecologic laparoscopic surgery. The present paper describes with help of transesophageal echocardiography the pressure relationship between the atria during laparoscopic surgery and the effect of volume preload. Methods: Twenty-one gynecologic ASA 1–3 patients were included in this open study. The movement of interatrial septum was monitored with transesophageal echocardiography during the procedure. If the septum movement was to the left, the patient was given 500 mL hydroxyethyl starch to increase the filling pressures. Results: After induction, the mobile part of foramen ovale rounded to the right in 15 patients but six patients showed movement to the left. After pneumoperitoneum and head-down tilt, one patient of the six returned to normal but eight additional patients showed movement to the left. These 13 patients had a filling infusion of 500 mL hydroxyethyl starch. The movement was normalized in 12 patients. We saw echogenic particles coming from the inferior caval vein in every patient. Only one patient had very small atrial septal defects and no embolic complications. Conclusion: The head-down tilt and pneumoperitoneum had a more negative influence on the filling of the left side than on the filling of the right side of the heart. The pressure reversal occurs in systole during expiration of mechanical ventilation. The infusion of volume helps to normalize the pressure relationship and to diminish the embolic risk.