We report a case of an infected aortic pseudoaneurysm caused by delayed sternal osteomyelitis. A 79-year-old man underwent combined surgery comprising aortic valve replacement (AVR), coronary artery bypass grafting (CABG) and permanent pacemaker implantation at our department due to aortic insufficiency (third degree), coronary sclerosis, and sick sinus syndrome (type 1). The subject was discharged home on postoperative day (POD) 27. Sternal osteomyelitis developed on POD 50, and the subject was re-hospitalized. However, on day 6 of readmission, auscultation revealed a new systolic murmur (Levin IV/VI) in the second right intercostal space sternal border and transthoracic echocardiography showed abnormal blood flow from the base of the aorta to the left front. Contrast-enhanced computed tomography (CT) revealed an infected pseudoaneurysm of the ascending aorta that was not detected by CT at readmission. An infected aortic pseudoaneurysm caused by delayed sternal osteomyelitis was diagnosed. On day 8 of readmission, the pseudoaneurysm was excised and the ascending aorta was replaced. Intraoperative findings revealed that the aortic pseudoaneurysm had formed from the site of the ascending aorta anastomosis at the time of performing AVR and that part of the aneurysm had perforated into the right ventricular outflow tract. In the present case, the new cardiac murmur identified on auscultation and consequently performing echocardiography at the bedside led to the definitive diagnosis.