An unusual case of left ventricular outflow tract obstruction associated with severe left ventricular failure in a neonate is reported. The physical and laboratory data were consistent with the diagnosis of infantile valvular aortic stenosis. At operation, however, redundant gelatinous pedunculated tissue attached to the mitral valve annulus appeared to move through and obstruct the aortic valve during systole. The aortic valve showed only minimal thickening of the right and left coronary cusps. A distinct angiographic pattern was demonstrated during left ventricular cineangiography. In the frontal projection a large ovoid filling defect appeared to protrude through the aortic valve during systole and return to a subvalvular location during diastole. Recognition of this angiographic pattern should facilitate diagnosis and subsequent repair. Complete correction is possible by operative excision of the obstructing tissue without damaging the mitral valve. In contrast to isolated congenital infantile valvular aortic stenosis, a condition in which the valve leaflets are often primitive and deformed, aortic valvotomy and/or subsequent valve replacement are not necessary, resulting in a better long-term prognosis.