Further to some of the comments, you may actually want to hit a bit higher to make sure that you get both lungs. If you aim for the heart, it's low in the chest cavity and you could end up with a single lung hit rather than a double lung just because of the angle of the shot. Another issue to think about is close shots under 10 yds and especially under 5 yards. Most people have limited experience with this shot and if presented with the shot will miss low. This is a shot that is possible from a tree stand and has NOTHING to do with the stand height, it relates to what's technically known as parallax. Parallax is the distance from the initial line of arrow travel to the line of sight. This can be 3-6" depending on how you've set up your bow.
One other thought, most people put too much heel into the grip causing high misses also, this is usually the result of draw length being incorrect. And at the risk of being blasphemous, most pro's shooting field today in Europe don't bend at the waist they rely on correct draw length, solid walls & proper peep positioning on the string to get everything right. The whole reason every one has been told to bend at the waist was to keep all of the geometry right and you can eliminate one of the factors just by shooting hard against the wall. The other one, draw length seems to be a tough one - most people are positive their draw length is good already
even though changes as small as 1/8" can make big differences.