A 76-year-old woman with a history of non-valve atrial fibrillation (AF), hypertension, diabetes, prior ischemic stroke, a CHA2DS2-VASc score of 7, and a HAS-BLED score of 3 underwent percutaneous LAAC for secondary prevention of stroke. The LAAC procedure was performed under local anesthesia, deep sedation, and fluoroscopic guidance. A decapolar catheter was inserted through the right femoral vein into the coronary sinus to guide transseptal puncture. Unfractionated heparin (100 U/kg) was administered immediately following transseptal puncture to achieve an activated clotting time of 330 s. The left atrial pressure was 33/15 mmHg. Left atrial appendage (LAA) angiography ( and ) at the right anterior oblique 30° and caudal 20° view revealed ostial width of 19.5 mm and depth of 21.8 mm. A 24-mm Watchman device (Boston Scientific, MA, United States) was selected and then deployed under fluoroscopic guidance. Post-deployment angiography revealed brisk contrast extravasation into the pericardial space ( and ). The patient rapidly developed cardiac tamponade, and blood pressure decreased from 131/72 to 78/35 mmHg. We performed emergency pericardiocentesis via a subxiphoid approach under fluoroscopic guidance. A pigtail catheter was inserted into the pericardial cavity to drain blood, and the aspirated pericardial blood was immediately returned to the femoral vein via a sheath. Protamine (30 mg) was simultaneously administered to reverse heparin activity. The patient’s systolic blood pressure returned to 95 mmHg after aspiration of 150 ml of blood. The device was retracted and redeployed at a more proximal position to effectively seal the LAA and distal perforation ( and ). After confirmation of device stability and absence of residual peri-device leakage, the Watchman device was released ( and ). Repeat aspiration was performed for an additional 15 min. The patient’s vital signs stabilized, and blood pressure returned to 120/65 mmHg. The pericardial fluid was drained to dryness after aspiration of 400 ml of blood, and minimal pericardial fluid reaccumulation was observed. Following 10 min observation, the patient’s heart rate showed intermittent slowing with a decrease in blood pressure to 90/62 mmHg. A temporary pacing lead was placed into the right ventricular to maintain a ventricular rate of > 60 beats per minute. Fluoroscopy revealed a near-normal-sized cardiac silhouette ( and ), and minimal pericardial blood was drained after the insertion of a new pigtail catheter. The decrease in blood pressure was likely attributable to suspected pericardial thrombosis. Emergency echocardiography revealed a hypoechoic (rather than anechoic) effusion in the pericardial space (), suggestive of early pericardial thrombosis. The emergency surgical team was summoned to prepare for open chest surgery. The patient’s blood pressure was temporarily stable at approximately 90/60 mmHg; therefore, intrapericardial thrombus aspiration was attempted before surgery. However, thrombus aspiration failed using a pigtail catheter, which was replaced by an 8.5 F long sheath (SL1, Abbott, MN, United States). Unfortunately, thrombus aspiration through the sheath was also unsuccessful. Thereafter, we used a dedicated thrombus aspiration catheter. A 6F guiding catheter (Judkins R4.0, Medtronic, MN, United States) was inserted through the long sheath into the pericardial cavity via an angioplasty guidewire (BMW, 0.036 cm × 190 cm, Abbott, MN, United States), and a thrombus aspiration catheter (Thrombuster II, Kaneka Medical Products, Osaka, Japan) was advanced into the pericardial cavity via the guidewire. Following manipulation of the guiding catheter and guidewire, we could maneuver the thrombus aspiration catheter to successfully aspirate the thrombus from multiple sites across the pericardium ( and, ). Sludge-like blood (instead of a thrombus) was drained using the aspiration catheter (). We aspirated 120 ml of sludge-like blood after 10 min. The patient was hemodynamically stable, and blood pressure returned to 123/62 mmHg. Echocardiography revealed mild effusion and a round hyperechoic thrombus (2.5 cm × 1.7 cm) in the vicinity of the right ventricular apex (). A pigtail catheter was placed to monitor the pericardium, and the patient was transferred back to the ward. The pigtail catheter was removed on the second postoperative day after echocardiography confirmed the absence of pericardial fluid reaccumulation. We observed shrinkage of the round thrombus, which appeared as a strip that measured 1.8 cm × 0.7 cm in size near the right ventricular apex ( and ). Anticoagulation was re-initiated on the third postoperative day, and the patient was discharged on the fifth postoperative day. Echocardiography performed 2 weeks after discharge revealed no thrombus or pericardial effusion ( and ), and the patient had no thromboembolic event or pericardial effusion during 1-year follow-up.