A 72-year-old man with persistent pericarditis who had been treated for Dressler’s syndrome but did not show improvement of symptoms was transferred to our hospital. He had had right coronary artery stenting for ST-elevation myocardial infarction a month earlier and was prone to cholangitis. An echocardiogram revealed decreased pericardial effusion, and Escherichia coli was detected in a blood culture test after admission. Because the patient had cholangitis, endoscopic retrograde cholangiopancreatography (ERCP) was performed. Blood tests revealed elevated levels of myocardial enzymes and inflammatory markers even after ERCP and antibiotic treatment. An echocardiogram was performed to confirm increased pericardial effusion. Computed tomography revealed a 3-cm-sized contrast-enhanced lesion around the right coronary artery (Fig. 1). Consequently, coronary angiography was performed, and a massive right coronary aneurysm near the previous stent was confirmed (Fig. 2), indicating a mycotic coronary aneurysm. Thus, we decided to perform coronary artery bypass surgery with aneurysm resection. Massive adhesions and abscess formation were detected when the pericardium was dissected, and the ruptured aneurysm was discreetly covered by the brittle adhesive inflammatory pericardium. The final echocardiogram revealed no pericardial effusion after 4 weeks of antibiotic treatment.