Bowhunters should always strive for quick, humane kills by holding out for double-lung or heart shots. The higher you set your stand, however, the smaller the vital zone becomes. Broadside at ground level, an average whitetail's vital zone is an irregularly shaped, 8-by 8-inch target. As tree-stand height increases, the shielding effect of the spine and scapular bones along with the narrowing chest cavity cause that zone zone to shrink. From 30 feet up, a deer standing 10 yards away presents a 45-degree shot angle with a target measuring on average only 6 by 4 inches--a 62 percent reduction in the size of the kill zone. Any higher and the angle becomes too steep and the target area too small for an acceptable margin of error.