In patients with ischemic stroke more than 17 % have atrial fibrillation. Oral anticoagulant therapy is the main strategy for embolism prevention in patients with atrial fibrillation. In the presence of contraindications, an alternative to anticoagulant therapy is isolation of the left atrial appendage. The use of the left atrial appendage occluder is comparable in effectiveness to the prevention of ischemic stroke using anticoagulant therapy. However, possible complications arising from device implantation remain a limitation to the spread of this method. The article presents a clinical observation of a 55-year-old patient who was admitted to the hospital for a planned intervention — endovascular implantation of the Watchman device (Boston Scientific, USA). The development of atrial fibrillation was induced by acute myocardial infarction in 2016. In 2019, the patient underwent ischemic stroke in the territory of the right middle cerebral artery. The indication for implantation was recurrent gastroduodenal bleeding while taking oral anticoagulants. During the implantation stage, the delivery system was dislocated into the pericardial cavity. In connection with the frolicking complication, a decision was made to drain the pericardium with repositioning and subsequent implantation of the Watchman to close the left atrial appendage defect. Despite the frolic complication, left atrial appendage isolation was achieved. This prevented the development of massive hemopericardium and cardiac tamponade. The patient fully returned to normal life and self-care, the modified Rankin score was 190 days after the surgery. During the 10-month follow-up, the patient did not experience cardiovascular events and major bleeding, which indirectly indicates the effectiveness of left atrial appendage occlusion, despite the developed complication.