One of the classical signs described during cardiac catheterisation in aortic stenosis is the “Prussian helmet” sign. In “pure” aortic stenosis with no concomitant aortic regurgitation, aortography often demonstrates a negative jet of radiolucent blood exiting focally from the left ventricle. In congenital aortic stenosis (secondary to bicuspid aortic valve in this particular case), there may be upward doming of the aortic valve leaflets which together with the central negative jet gives the so called Prussian helmet sign named after the lobster tail helmet used by the Prussian army. This patient underwent subsequent successful balloon aortic valvoplasty.