Abstract
It is now possible to synthesize the natural history of ventricular septal defect. Size is fundamental, and stemming from it, the smaller defects (groups 1 and 2) separate from the larger (groups 3, 4, and 5) immediately at birth. Apparent size may differ from real size, for defects may become partially closed by tricuspid valve leaflets, or be gradually obstructed by an enlarging aneurysm of the sinus of Valsalva. One instance has been observed in which a muscular defect was obstructed by a large papillary muscle. The reverse may also occur, i.e., a partially obstructed defect may enlarge as a blocking tricuspid leaflet detaches or tears.