2 Samuel 18:14

three darts Since the word used means elsewhere rodsor staves(Exodus 21:20; 2 Samuel 23:21), and the wounds inflicted were not at once mortal, it seems that Joab struck Absalom brutally with pointed wooden staves, the first weapons which came to hand, in fact in a kind of way impaledhim as a traitor, and left his squires to give him the coup de grâce.

through the heart Not literally through his heart, for the blows did not kill him outright; but into the midst of his body.