This report details a case of intraoperative acute cardiac tamponade caused by left atrial perforation during a percutaneous intervention for anomalous pulmonary venous return, a rare but life-threatening complication. Despite emergency measures including continuous pericardiocentesis and an open sternotomy for repair, the patient, an 86-year-old female with history of right-ventricular failure and atrial fibrillation, succumbed to her condition hours post-operation. The case emphasizes the critical need for swift, multidisciplinary intervention in managing such complications and outlines the potential risks associated with percutaneous cardiac procedures.