Propionibacterium acnes typically colonizes the orophar- ynx and skin but may cause postoperative infections and opportunistic infections, especially when a foreign device is present. We report a case of pericarditis due to P. acnes complicated by tamponade. ericarditis is characterized by inflammation within the peri- cardium due to an infectious or noninfectious etiology. Idi- opathic pericarditis and viral pericarditis, which are the most common forms of pericarditis seen in the postYantibiotic era, have self-limited courses in contrast to purulent pericarditis, which presents with a more fulminant course and high mortal- ity. 1 Purulent pericarditis is defined as gross or microscopic purulence in the pericardium. 1 Although it is unusual for the pericardium to be a site of infection, reports of purulent peri- carditis date back to the time of Galen. 2 Current medical so- phistication, including open heart surgery and placement of prosthetic devices, has led to an increasing number of pericar- ditis cases, including those due to anaerobic bacteria. 3 Because anaerobic bacteria have been an uncommon cause of pericardi- tis historically, anaerobes are frequently not sought as clinicians search for an etiology. The purpose of this case presentation was to increase the clinician's awareness of anaerobic bacteria as causes of pericarditis and to illustrate the need for meticulous microbiologic technique to enhance isolation. We report a case of purulent pericarditis due to a representative anaerobe, Pro- pionibacterium acnes. The patient had previously been a significant consumer of alcohol and tobacco (45-pack-year history). He resided in an urban section of Louisville and was unemployed after having been a forklift operator. He had no history of travel to foreign countries, had no recent travel outside of Kentucky, and owned no pets. On admission, the patient's vital signs were as follows: tem- perature, 97.9-F; pulse, 126 beats/min; respirations, 28 breaths/min; and blood pressure, 135/102 mm Hg. His physical examination was notable for poor dentition. The cardiac examination revealed jugular venous distention and indistinct heart sounds. Crackles were detected bilaterally in the lungs. The abdomen was dis- tended while edema was present in the lower extremities. The dermatologic, musculoskeletal, and neurological examinations were unremarkable. The initial diagnostic workup revealed a normal complete blood count, normal electrolytes, and normal kidney and liver function tests. However, the brain natriuretic peptide level was elevated at 609 pg/mL (reference range, 0Y300 pg/mL). The electrocardiogram revealed sinus tachycardia and a low QRS voltage. The chest roentgenogram showed cardiac enlargement with bilateral pleural effusions, whereas computed tomography of the chest and abdomen was notable for a large pericardial effusion, bilateral pleural effusions, and abdominal ascites. No masses or lymphadenopathy were detected. The patient was admitted to the cardiac care unit, and a