A 41-year-old man sought evaluation at the emergency department for pain in the anterior chest that had been ongoing for approximately 35 hours. The electrocardiogram showed marked ST segment elevation in the precordial leads. Cardiac biomarker levels were elevated. He subsequently underwent coronary angioplasty and stenting of the left anterior descending artery using two sirolimus-eluting stents. The following day, the patient complained of severe pain in his chest and shoulders. Computed tomography (CT) of the chest showed small gas bubbles around the aortic wall and mild pericardial thickening with subtle air densities, suggesting acute mediastinitis. With an impression of postcardiac injury syndrome and acute mediastinitis, he was treated with intravenous antibiotics and oral ibuprofen. Two days later, the patient had subjective improvement and the friction rub was no longer heard.