Aneurysm of the membranous septum in critical pulmonary stenosis: spontaneous rupture after balloon dilatation.

We report a case of critical pulmonary valve stenosis in which congenital aneurysm of the membranous septum ruptured spontaneously after balloon dilatation of the pulmonary valve. It is considered that the chronic mechanical trauma with phasic protrusion and collapse of the aneurysm during the cardiac cycles was responsible for an aneurysm rupture.