A 49-year-old-woman who had had a pacemaker implanted 15 years earlier became acutely ill with a continuous high fever and general fatigue. A pulmonary artery aneurysm had been rapidly developing and had arrived at the acute phase within 2 weeks. After removal of the pacemaker and with antibiotic therapy the aneurysm gradually decreased in size and has been without rupture for 3 years. Conservative treatment seemed to be sufficient for the management of a mycotic aneurysm in this case.