Aneurysms of the sinus of Valsalva are rare, with dissecting aneurysms of the sinus of Valsalva that extend into the interventricular septum being even more rare. This report describes a young patient with syphilis and a quadricuspid aortic valve who experienced a spontaneously dissecting aneurysm of the sinus of Valsalva and the basal interventricular septum.