Anorexia nervosa (AN) is a complex psychiatric disorder that can have devastating cardiovascular complications. Its lesser-known association with pericardial effusion has been recently described in the literature. We present the case of a 45 year-old female who presented with a recurrent small bowel obstruction requiring lysis of adhesions and who was found to have a large pericardial effusion that progressed to cardiac tamponade necessitating surgical intervention. The patient had a body mass index of 14.8 kg/m2 (i.e. 71% of ideal body weight) and a long-standing history of food aversion, extreme exercise habits, and weight obsession consistent with AN. To the best of our knowledge, this is the first case of AN-associated cardiac tamponade in the United States, and the first requiring surgical intervention. In conclusion, with this and current data regarding AN-associated pericardial effusions, we recommend a low threshold for performing pre-operative echocardiography for those in whom AN is suspected.