This is a great cut away that Woody Sanford of Magnus Broadheads made picture by picture to show true anitomical content.

QUOTE
The distance between the humorus and the ribcage runs about 4-5.5" on mature black bears and 7-9 on a mature interior griz. Attempting to shoot up tight to the shoulder like you do on deer can cause you to miss the vitals altogether, passing through between the ribcage and leg. The majority of those shot and lost here in AK over baits are shot just like this.
The point of center for the heart averages roughly 7-8cm behinde the shoulder line of a standing broadside bear, so on bears you need to back off the shoulder a bit to "center punch" the vitals. There is a misconception that bears don't bleed very well. Bear hair does not shed blood or water very well but if you do hit them well you will still have a good blood trail.