Background <p>Congenital pericardial defect (CPD) is a rare congenital heart malformation with atypical clinical symptoms.</p> Case presentation <p>The 69-year-old woman was referred because a 23-mm mixed ground glass shadow was found in the apicoposterior segment (S^1 + 2) of the left lung. The S^1 + 2 segment excision of the left upper lung was performed under uni-portal fluorescence thoracoscopy. Intraoperatively, an unintentional complete absence of the pericardium was discovered, with the phrenic nerve running behind the sternum. To reduce the intraoperative stimulation of the heart and prevent postoperative friction of the bronchial stump against the left atrial appendage, the pulmonary hilum was not separated, and the intersegmental vein (V^1 + 2b + c) was not cut off. Given the patient’s lack of symptoms and the low risk of cardiac hernia, no specific pericardial surgery was performed. The patient was well at the 1-month postoperative follow-up.</p> Conclusions <p>This paper reports a case of complete pericardial defect accidentally found during left upper lung S^1 + 2 segmentectomy under single-hole thoracoscopy, summarizes the main points of diagnosis and surgical precautions, and provides experience reference for similar clinical cases.</p>