Pericardial effusion is frequently found in patients diagnosed with hypothyroidism, yet it is rarely associated with cardiac tamponade. This report presents an atypical case concerning a 60-year-old Taiwanese female, with a history of thyroidectomy surgery due to thyroid cancer, who was later diagnosed with myxedema and cardiac tamponade. Treatment included an immediate pericardiocentesis followed by thyroxine hormone replacement therapy. Postoperative and recovery phases progressed favorably, and the patient's prognosis is good.