A 43-year-old man who had a Carbomedics prosthetic aortic valve replacement in 1997 was admitted to our hospital with complaints of shortness of breath and dyspnea on exertion in 2000. The patient was hospitalized due to atrioventricular (AV) complete block and a permanent pacemaker was implanted. At that time echocardiography indicated an aneurysm at the left sinus of Valsalva. In 2003, the patient was re-admitted to our clinic with complaints of shortness of breath and fatigue. Echocardiography showed a sinus of Valsalva aneurysm dissecting into interventricular septum. Operation confirmed dissection of the interventricular septum and communication between this cavity and the aneurysm of the left sinus of Valsalva. The postoperative course was uneventful and the patient was discharged in a satisfactory condition. This is the first reported case of aneurysm of the sinus of Valsalva dissecting into interventricular septum late and complicating aortic valve replacement.