Mycotic aneurysm is a rare, life-threatening condition with high mortality rates and challenging diagnosis. A 46-year-old man, with a history of subaortic membranectomy, was admitted with a new onset fever and dyspnea. Transesophageal echocardiography and computed tomography demonstrated a mycotic pseudoaneurysm of the ascending aorta and mediastinal abscess due to aneurysm rupture. The patient fully recovered after an immediate diagnose and urgent surgery.