This study was performed to investigate the safety and efficacy of a method using free pericardial fat pads as a sealant to prevent intraoperative and postoperative alveolar air leaks. Animal experiments were performed. After pulmonary parenchymal defects were created in 4 dogs, the alveolar air leaks were sealed with free pericardial fat pads. Clinical application was applied in 23 patients who underwent pulmonary resection, air leaks with stream of bubbles, or worse, were sealed with free pericardial fat pads. All dogs survived for 1 month without complications. At sacrifice, all treated lungs had expanded adequately and the implanted fats remained on the lung surface. Histologic examination showed that the excised edge of the lung was closed with granulation. The clinical outcome showed the mean duration of air leaks, chest drain, and postoperative hospitalization were 2.3 +/- 3.1 days, 4.3 +/- 3.2 days, and 11.1 +/- 3.7 days, respectively. Recurrent air leaks were not observed after removal of the chest tube. No adverse effects were observed after surgery. The use of free pericardial fat pads was able to successfully prevent alveolar air leaks.