A 29-year-old gravida 1, para 0 patient was admitted at 31 weeks gestation with hypertension, proteinuria and generalized edema. Three days after admission, she developed cardiac tamponade, a severe form of preeclampsia, and premature labor. Anesthesia for pericardiocentesis consisted of local anesthetic infiltration of the anterior chest wall, supplemented with an oxygen mask(5 L/min). After drainage of pericardial fluid, emergency cesarean section was performed under general anesthesia. After surgery, she was studied for the cause of the cardiac tamponade, and subsequently was diagnosed to have hypothyroidism. Pericardial effusion as a hypothyroidism associated sign, is something that is frequently found; nevertheless, cardiac tamponade as the first sign of this disease may be considered exceptional especially in a pregnant woman. We exprienced a case of hypothyroidism during a 29-year-old woman's first pregnancy, complicated by a severe form of preeclampsia and pericardial effusion.