MLN, It's what I've always heard, and from the deer I have field dressed, it seems to be pretty close. Might be a bit larger than that, but a 7 inch circle is a good guage. The heart is about the size of my fist, the lungs stick up above and behind the heart about the same distance, so maybe an 8-9 inch circle. Larger animals like elk go up to about 14 inches. Granted, the bigger the deer, the bigger the kill zone. The average I have shot the last few years have been over 250#, and they were roughly a 9 inch circle. Just hit them in the lower half, and watch them drop. Hit them high, and they'll take a while longer to drop, and leave far less of a blood trail.