I made this rough diagram for you guys:
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The
red squiggles are the major Anterior Spinal arteries than Sakura sliced through. The
white lines are the several ribs that Sakura had to shatter and move in order to reach into the chest cavity, and the
yellow blob is Naruto's left lung, which Sakura would've had to punch through in order to reach the heart located behind it.
Sakura is now currently contracting the heart from all sides with her fist, which is actually far less effective than standard chest compressions. This action is causing him to continuously bleed out of the gaping external and internal wounds she just created.
Do you know what she could've done better? ****ing CPR. Seriously, there's a reason doctor's don't do this in real life. Because it's retarded.
Clearly she hasn't learned a damn thing from Tsunade as far as standard EMPs are concerned, since even 12 year-olds know how to perform chest compressions.