Aortic stenosis is a relatively common lesion in childhood. In severity, it may vary from extreme mildness to cases terminating in sudden death. The prognosis is worse in the presence of left ventricular strain as shown by the electrocardiogram. Progression of signs of left ventricular "strain" by electrocardiogram should be studied by catheterization of the left side of the heart prior to deciding upon aortic valvotomy.