Dissection of the interventricular septum by aneurysm of sinus of Valsalva is a rare lesion and has poor prognosis. However, it can be diagnosed noninvasively with echocardiography and managed well by surgical repair. A 55 year old female was readmitted due to aggravated exertional dyspnea. She was implanted with permanent pace-maker due to complete atrioventricular (AV) block of recent onset at a community hospital. Previous diastolic murmur near aortic area was changed to a new continuous murmur. The diagnosis of an aneurysm of sinus of Valsalva dissected into the interventricular septum was confirmed by routine two-dimensional echocardiography. The neck of the aneurysm was closed primarily with patch and aortic valve replacement was done. The pro-gnosis was good. The finding of AV block of recent onset and obscure origin in a young patient should alert the physician to the possibility of an aneurysm of sinus of Valsalva and warrants systematic echocardiography.