OBJECTIVE The LigaSure device has been demonstrated to be safe for systemic vessels up to 7 mm in diameter, although its use in thoracic surgery remains understudied. We aimed to evaluate the safety of LigaSure for pulmonary artery sealing. METHODS In 30 cases of open lung lobectomy, 15 small pulmonary arteries (diameter, 3-5 mm) and 15 thick pulmonary arteries (diameter, 6-8 mm) were divided with LigaSure. Before closure of the thoracotomy, the vessel stumps were ligated proximal to the sealing zone, resected, and preserved in formaldehyde for histopathologic examination. In a control group, a similar number and size of pulmonary arteries were suture-ligated. The burst pressure of the pulmonary arteries from the resected lung lobes was measured. RESULTS The mean burst pressure of small pulmonary arteries was 4.3-fold less after sealing than after ligation (315 ± 213.1 mm Hg vs 1345 ± 256 mm Hg; P < .001), and 6.4-fold less than after ligation of thick pulmonary arteries (156 ± 42.5 mm Hg vs 1007 ± 141.6 mm Hg; P < .001). Sealed pulmonary arteries >5 mm in diameter have a burst pressure that is 50% less than that of smaller arteries (P < .001). In all cases after sealing, the histologic examination demonstrated only a fusion of the adventitia, whereas the intima and media were replaced and invaginated into the vessel lumen. CONCLUSIONS LigaSure does not result in complete fusion of the wall layers of pulmonary arteries. The pulmonary artery burst pressure after sealing is significantly less compared with conventional suture ligation. It remains unclear whether these findings create a clinical risk of rupture.