LESIONS of the left side of the heart, both congenital and acquired, demand precise physiologic and anatomic diagnosis for accurate surgical relief. This is especially true in infants and children. The development of technics for catheterization of the left side of the heart has made such a goal possible.1 Percutaneous intubation of a cardiac catheter in the adult preserves the integrity of the artery. In infants and children this is not always possible because of the small size of the arterial lumen. Cutdown and exposure of the brachial or superficial femoral artery is usually necessary. Direct transverse or longitudinal . . .